The disintegration of Jake’s life took him by surprise. It happened early in his junior year of high school, while he was taking three Advanced Placement classes, running on his school’s cross-country team and traveling to Model United Nations conferences. It was a lot to handle, but Jake — the likable, hard-working oldest sibling in a suburban North Carolina family — was the kind of teenager who handled things. Though he was not prone to boastfulness, the fact was he had never really failed at anything.

Not coincidentally, failure was one of Jake’s biggest fears. He worried about it privately; maybe he couldn’t keep up with his peers, maybe he wouldn’t succeed in life. The relentless drive to avoid such a fate seemed to come from deep inside him. He considered it a strength.

Jake’s parents knew he could be high-strung; in middle school, they sent him to a therapist when he was too scared to sleep in his own room. But nothing prepared them for the day two years ago when Jake, then 17, seemingly “ran 150 miles per hour into a brick wall,” his mother said. He refused to go to school and curled up in the fetal position on the floor. “I just can’t take it!” he screamed. “You just don’t understand!”

Jake was right — his parents didn’t understand. Jake didn’t really understand, either. But he also wasn’t good at verbalizing what he thought he knew: that going to school suddenly felt impossible, that people were undoubtedly judging him, that nothing he did felt good enough. “All of a sudden I couldn’t do anything,” he said. “I was so afraid.” His tall, lanky frame succumbed, too. His stomach hurt. He had migraines. “You know how a normal person might have their stomach lurch if they walk into a classroom and there’s a pop quiz?” he told me. “Well, I basically started having that feeling all the time.”

Alarmed, Jake’s parents sent him to his primary-care physician, who prescribed Prozac, an antidepressant often given to anxious teenagers. It was the first of many medications that Jake, who asked that his last name not be used, would try over the next year. But none seemed to work — and some made a bad situation worse. An increase in dosage made Jake “much more excited, acting strangely and almost manic,” his father wrote in a journal in the fall of 2015. A few weeks later, Jake locked himself in a bathroom at home and tried to drown himself in the bathtub.

He was hospitalized for four days, but soon after he returned home, he started hiding out in his room again. He cried, slept, argued with his parents about going to school and mindlessly surfed the internet on his phone. The more school he missed, the more anxious he felt about missing school. And the more anxious he felt, the more hopeless and depressed he became. He had long wanted to go to the University of North Carolina at Chapel Hill, but now that felt like wishful thinking.

Not every day was bad. During spring break in 2016, Jake’s father wrote: “Jake was relaxed and his old sarcastic, personable, witty self.” A week later, though, Jake couldn’t get through a school day without texting his mother to pick him up or hiding out in the nurse’s office. At home, Jake threatened suicide again. His younger siblings were terrified. “It was the depth of hell,” his mother told me.

That summer, after two more hospitalizations, Jake’s desperate parents sent him to Mountain Valley in New Hampshire, a residential treatment facility and one of a growing number of programs for acutely anxious teenagers. Over the last decade, anxiety has overtaken depression as the most common reason college students seek counseling services. In its annual survey of students, the American College Health Association found a significant increase — to 62 percent in 2016 from 50 percent in 2011 — of undergraduates reporting “overwhelming anxiety” in the previous year. Surveys that look at symptoms related to anxiety are also telling. In 1985, the Higher Education Research Institute at U.C.L.A. began asking incoming college freshmen if they “felt overwhelmed by all I had to do” during the previous year. In 1985, 18 percent said they did. By 2010, that number had increased to 29 percent. Last year, it surged to 41 percent.

Those numbers — combined with a doubling of hospital admissions for suicidal teenagers over the last 10 years, with the highest rates occurring soon after they return to school each fall — come as little surprise to high school administrators across the country, who increasingly report a glut of anxious, overwhelmed students. While it’s difficult to tease apart how much of the apparent spike in anxiety is related to an increase in awareness and diagnosis of the disorder, many of those who work with young people suspect that what they’re seeing can’t easily be explained away. “We’ve always had kids who didn’t want to come in the door or who were worried about things,” says Laurie Farkas, who was until recently director of student services for the Northampton public schools in Massachusetts. “But there’s just been a steady increase of severely anxious students.”

For the teenagers who arrive at Mountain Valley, a nonprofit program that costs $910 a day and offers some need-based assistance, the center is usually a last resort after conventional therapy and medications fail. The young people I met there suffered from a range of anxiety disorders, including social anxiety, separation anxiety, post-traumatic stress disorder and obsessive-compulsive disorder. (Though OCD and PTSD are considered anxiety disorders at Mountain Valley and other treatment centers, they were moved into separate categories in the most recent edition of the Diagnostic and Statistical Manual of Mental Disorders.)

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Sharon McCallie-Steller, a therapist, during a counseling session at the Mountain Valley residential program in New Hampshire.CreditSasha Rudensky for The New York Times

Mountain Valley teenagers spend a lot of time analyzing — and learning to talk back to — their anxious thoughts. During one group session in the summer of 2016 in a sunlit renovated barn with couches, a therapist named Sharon McCallie-Steller instructed everyone to write down three negative beliefs about themselves. That’s an easy exercise for anxious young people (“Only three?” one girl quipped), but McCallie-Steller complicated the assignment by requiring the teenagers to come up with a “strong and powerful response” to each negative thought.

She asked for volunteers. First, residents would share their negative beliefs and rebuttals with the group. Then others would act those out, culminating in a kind of public performance of private teenage insecurity.

Jake raised his hand. By then, he was in his third month at Mountain Valley, and he looked considerably less anxious than several of the newcomers, including one who sat slumped on a couch with his head in his hands. “I’m free to play the part of terrible, evil thoughts for anyone who needs them,” Jake said with a smile. He had already spent weeks challenging his own thinking, which often persuaded him that if he failed a single quiz at school, “then I’ll get a bad grade in the class, I won’t get into the college I want, I won’t get a good job and I’ll be a total failure.”

At Mountain Valley, Jake learned mindfulness techniques, took part in art therapy and equine therapy and, most important, engaged in exposure therapy, a treatment that incrementally exposes people to what they fear. The therapists had quickly figured out that Jake was afraid of failure above all else, so they devised a number of exercises to help him learn to tolerate distress and imperfection. On a group outing to nearby Dartmouth College, for example, Jake’s therapist suggested he strike up conversations with strangers and tell them he didn’t have the grades to get into the school. The college application process was a source of particular anxiety for Jake, and the hope was that he would learn that he could talk about college without shutting down — and that his value as a person didn’t depend on where he went to school.

Though two months in rural New Hampshire hadn’t cured Jake of anxiety, he had made significant progress, and the therapy team was optimistic about his return home for his senior year. Until then, Jake wanted to help other Mountain Valley teenagers face their fears.

Among them was Jillian, a 16-year-old who, when she wasn’t overwhelmed with anxiety, came across as remarkably poised and adultlike, the kind of teenager you find yourself talking to as if she were a graduate student in psychology. Jillian, who also asked that her last name not be used, came to Mountain Valley after two years of only intermittently going to school. She suffered from social anxiety (made worse by cyberbullying from classmates) and emetophobia, a fear of vomit that can be so debilitating that people will sometimes restrict what they eat and refuse to leave the house, lest they encounter someone with a stomach flu.

Jillian listened as Jake and other peers — who, in reality, liked her very much — voiced her insecurities: “I can’t believe how insignificant Jillian is.” “I mean, for the first three weeks, I thought her name was Susan.” “If she left tomorrow, maybe we wouldn’t even miss her.”

At the last one, Jillian’s shoulders caved, and her eyes watered. “I don’t want to do this,” she said, looking meekly at McCallie-Steller.

“If it’s too much, you can stop,” the therapist said, but Jillian considered the offer only long enough to reject it. She straightened her back. “No, I feel like I need to do this,” she announced. “I have a week and a half left. If I can’t get through something like this here …”

Her voice trailed off, but the implication was clear: The real world would be much more anxiety producing — and much less forgiving.

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Jillian in her room in Florida.CreditSasha Rudensky for The New York Times

Anxiety is the most common mental-health disorder in the United States, affecting nearly one-third of both adolescents and adults, according to the National Institute of Mental Health. But unlike depression, with which it routinely occurs, anxiety is often seen as a less serious problem.

“Anxiety is easy to dismiss or overlook, partially because everyone has it to some degree,” explained Philip Kendall, director of the Child and Adolescent Anxiety Disorders Clinic at Temple University in Philadelphia. It has an evolutionary purpose, after all; it helps us detect and avoid potentially dangerous situations. Highly anxious people, though, have an overactive fight-or-flight response that perceives threats where there often are none.

But sometimes there are good reasons to feel anxious. For many young people, particularly those raised in abusive families or who live in neighborhoods besieged by poverty or violence, anxiety is a rational reaction to unstable, dangerous circumstances. At the Youth Anxiety Center’s clinic in the Washington Heights neighborhood of Manhattan, which serves mostly poor and working-class Hispanic youth, teenagers would object to the definition of anxiety I heard often at Mountain Valley: “The overestimation of danger and the underestimation of our ability to cope.”

“The fears can be very real for our kids,” explained Carolina Zerrate, the clinic’s medical director. “Oftentimes their neighborhoods are not safe, their streets are not safe and their families can feel unsafe if there’s a history of trauma and abuse.” The contemporary political climate can also feel “incredibly unsafe for the community of kids we serve,” Zerrate adds, explaining that many have undocumented family members.

And yet addressing anxiety is low on the priority list in many economically disadvantaged communities. Kids who “act out” are often labeled defiant or aggressive, while those who keep to themselves — anxiety specialists call them “silent sufferers” — are overlooked or mistaken for being shy. “If you go to a public school in a struggling urban area, teachers will talk about drugs, crime, teen pregnancy, violence,” Kendall says. “When you start to talk about anxiety, they’re like, ‘Oh, those are the kids we like!’ ”

Teenagers raised in more affluent communities might seemingly have less to feel anxious about. But Suniya Luthar, a professor of psychology at Arizona State University who has studied distress and resilience in both well-off and disadvantaged teenagers, has found that privileged youths are among the most emotionally distressed young people in America. “These kids are incredibly anxious and perfectionistic,” she says, but there’s “contempt and scorn for the idea that kids who have it all might be hurting.”

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A resident taking part in equine therapy at Mountain Valley.CreditSasha Rudensky for The New York Times

For many of these young people, the biggest single stressor is that they “never get to the point where they can say, ‘I’ve done enough, and now I can stop,’ ” Luthar says. “There’s always one more activity, one more A.P. class, one more thing to do in order to get into a top college. Kids have a sense that they’re not measuring up. The pressure is relentless and getting worse.”

It’s tempting to blame helicopter parents with their own anxiety issues for that pressure (and therapists who work with teenagers sometimes do), but several anxiety experts pointed to an important shift in the last few years. “Teenagers used to tell me, ‘I just need to get my parents off my back,’ ” recalls Madeline Levine, a founder of Challenge Success, a Stanford University-affiliated nonprofit that works on school reform and student well-being. “Now so many students have internalized the anxiety. The kids at this point are driving themselves crazy.”

Though there are cultural differences in how this kind of anguish manifests, there’s considerable overlap among teenagers from different backgrounds. Many are anxious about school and how friends or teachers perceive them. Some obsess about family conflicts. Teenagers with OCD tend to worry excessively about what foods they should eat, diseases they might contract or whatever happens to be in the news that week. Stephanie Eken, a psychiatrist and the regional medical director for Rogers Behavioral Health, which runs several teenage-anxiety outpatient programs across the country and an inpatient program in Wisconsin, told me that in the last few years she has heard more kids than ever worry about terrorism. “They wonder about whether it’s safe to go to a movie theater,” she said.

When I asked Eken about other common sources of worry among highly anxious kids, she didn’t hesitate: social media. Anxious teenagers from all backgrounds are relentlessly comparing themselves with their peers, she said, and the results are almost uniformly distressing.

Anxious kids certainly existed before Instagram, but many of the parents I spoke to worried that their kids’ digital habits — round-the-clock responding to texts, posting to social media, obsessively following the filtered exploits of peers — were partly to blame for their children’s struggles. To my surprise, anxious teenagers tended to agree. At Mountain Valley, I listened as a college student went on a philosophical rant about his generation’s relationship to social media. “I don’t think we realize how much it’s affecting our moods and personalities,” he said. “Social media is a tool, but it’s become this thing that we can’t live without but that’s making us crazy.”

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A resident meditating during a yoga session at Mountain Valley.CreditSasha Rudensky for The New York Times

In his case, he had little doubt that social media made him more self-conscious. “In high school, I’d constantly be judging my self-worth online,” he told me, recalling his tortured relationship with Facebook. “I would think, Oh, people don’t want to see me on their timeline.”

While smartphones can provoke anxiety, they can also serve as a handy avoidance strategy. At the height of his struggles, Jake spent hours at a time on his phone at home or at school. “It was a way for me not to think about classes and college, not to have to talk to people,” he said. Jake’s parents became so alarmed that they spoke to his psychiatrist about it and took his phone away a few hours each night.

At a workshop for parents last fall at the NW Anxiety Institute in Portland, Ore., Kevin Ashworth, the clinical director, warned them of the “illusion of control and certainty” that smartphones offer anxious young people desperate to manage their environments. “Teens will go places if they feel like they know everything that will happen, if they know everyone who will be there, if they can see who’s checked in online,” Ashworth told the parents. “But life doesn’t always come with that kind of certainty, and they’re never practicing the skill of rolling with the punches, of walking into an unknown or awkward social situation and learning that they can survive it.”

Jean Twenge, a professor of psychology at San Diego State University who researches adolescent mental health and psychological differences among generations, used to be skeptical of those who sounded an alarm about teenage internet use. “It seemed like too easy an explanation for negative mental-health outcomes in teens, and there wasn’t much evidence for it,” she told me. She searched for other possible explanations, including economic ones. But the timing of the spike in anxious and depressed teenagers since 2011, which she called one of the sharpest and most significant she has seen, is “all wrong,” she said. “The economy was improving by the time the increase started.”

The more she looked for explanations, the more she kept returning to two seemingly unrelated trend lines — depression in teenagers and smartphone adoption. (There is significantly more data about depression than anxiety.) Since 2011, the trend lines increased at essentially the same rate. In her recent book “iGen,” and in an article in The Atlantic, Twenge highlights a number of studies exploring the connection between social media and unhappiness. “The use of social media and smartphones look culpable for the increase in teen mental-health issues,” she told me. “It’s enough for an arrest — and as we get more data, it might be enough for a conviction.”

Last fall, at a high school near the New Hampshire-Vermont border, I watched Lynn Lyons, a psychotherapist and author, deliver bad news to a packed auditorium of teachers and counselors. “We’re not getting the job done,” she said, pacing the stage at Fall Mountain Regional High School, where she had been asked to lead a professional-development training session about anxiety.

More than a decade ago, the school would have been unlikely to invite her to speak. Anxiety was barely on the radar of most educators back then, according to Denise Pope, another founder of Challenge Success, the Stanford-affiliated nonprofit. Pope remembers facing skepticism when she sounded the alarm about growing anxiety among teenagers. “We don’t have to convince them anymore,” she told me. “Schools are coming to us, eager for help.”

A gregarious speaker, Lyons kept her audience entertained by calling anxiety “the cult leader” — for its ability to convince people of falsehoods about themselves — and telling funny stories about overinvolved parents. But her main point was clear: In a seemingly well-meaning effort to help kids avoid what makes them anxious, administrators actually make anxiety worse. “Anxiety is all about the avoidance of uncertainty and discomfort,” Lyons explained. “When we play along, we don’t help kids learn to cope or problem-solve in the face of unexpected events.”

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Kids hanging out in the lounge after lunch at Mountain Valley.CreditSasha Rudensky for The New York Times

She pointed to the increasing use of “504 plans,” a popular educational tool that allows for academic accommodations for students with physical or mental disabilities. Though 504 plans for anxiety vary by student, a typical one might allow a teenager to take more time on homework and tests, enter the school through a back door — to avoid the chaos of the main entrance — and leave a classroom when feeling anxious.

Lyons believes in the necessity of 504 plans, and she is in agreement with many of the recommendations of Challenge Success, including later school start times, less homework and more project-based learning. But Lyons worries that too many 504 plans are “avoidance-based and teach zero skills.” She gave the example of a plan that allows a student to leave a classroom anytime he feels overwhelmed. Often, a teenager “can go wherever he wants and stay there for as long as he thinks he needs,” she said. Instead, she argued, a school should have a policy in place for the student to seek out a guidance counselor or nurse and do some role-playing that helps the student “externalize his worry,” similar to how Mountain Valley teenagers are taught to observe their thinking and talk back to it. Then the student should return to his regular classroom as soon as possible, Lyons said.

“If anxiety could talk, it would say, ‘You know, let’s just get out of here. We don’t have to do this!’ ” Lyons said from the stage. “But in order to retrain the brain, in order to create that message that says that even though I’m uncomfortable I can do this, we need to stop treating these anxious kids like they’re so frail, like they can’t handle things.”

Lyons sees a connection between how some schools deal with anxious students and what she worries is a generation of young people increasingly insistent on safe spaces — and who believe their feelings should be protected at all costs. “Kids are being given some really dangerous messages these days about the fact that they can’t handle being triggered, that they shouldn’t have to bear witness to anything that makes them uncomfortable and that their external environments should bend to and accommodate their needs,” she told me.

Among many teachers and administrators I spoke to, one word — “resiliency” — kept coming up. More and more students struggle to recover from minor setbacks and aren’t “equipped to problem-solve or advocate for themselves effectively,” a school counselor in suburban Oregon told me. In the last few years, the counselor said, she has watched in astonishment as more students struggle with anxiety — and as more of those “stop coming to school, because they just can’t.”

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A Mountain Valley resident doing art therapy.CreditSasha Rudensky for The New York Times

Some schools have taken drastic measures to accommodate what one administrator called “our more fragile students.” At Roxbury High School in Roxbury Township, N.J., there are two dedicated classrooms for anxious teenagers, including one next to a mural of Edvard Munch’s painting “The Scream.” These students typically avoid the mammoth school cafeteria in favor of eating lunch in one of the classrooms, as they did on the day of my visit last May. They had just finished gym class, an anxiety-producing event for some even as the school did all it could to reimagine the concept. Music blasted throughout the gym as the teenagers halfheartedly played something vaguely approximating a game of volleyball. The ball was allowed to bounce once before being struck — not that anyone was keeping score.

I couldn’t help wondering what Lyons, and other therapists I spoke to who worry that schools inadvertently worsen anxiety, would think of this approach. Some of the programs’ teenagers hoped to go to college, where no special classrooms would await them. How was this preparing them for that?

“Some will say that this feeds the monster,” concedes Patricia Hovey, director of special services at Roxbury High. “But you’ve got to start where the kids are, not where you are or where you want them to be. We’ve got to get them in the building. Many of our students simply don’t come to school if they have to spend all day in” general-education classes. Once the students are in school, Hovey explained, staff members can help them build the confidence and skills to eventually transition to Roxbury’s regular classes — and stand a chance at navigating college or a job once they graduate.

Even with the promise of a special classroom, getting anxious kids to Roxbury High each morning demands a herculean effort from the program’s teachers and therapists. During my visit, I watched them text and call several no-show students in an effort to coax them out of bed. They also regularly communicate with parents, talking them through what to say to a teenager who refuses to leave his room. Paul Critelli, one of the program’s teachers, told me that many parents feel overwhelmed trying to get two or three kids ready for school each morning, and that their instinct is often to “sacrifice the anxious kid” in order to avoid morning hysterics and keep the family train running on time.

Mostly, though, Critelli wants to talk to the anxious students. “What’s the issue today?” I heard him ask during a phone call with a sophomore boy, who had missed his scheduled bus and was presumably speaking to Critelli from underneath his sheets. The call was a “Hail Mary,” as Critelli put it, because while he suspects that the boy sleeps with the phone “right next to his face,” he rarely responds when he’s feeling anxious. “I appreciate you picking up — you don’t normally do that,” Critelli told him, mixing in positive affirmation with a call to action. The school would be sending another bus, and Critelli expected him to be on it.

Critelli looked for any opportunity to push students out of their comfort zones. During an informal study period after lunch, I watched him confiscate cellphones he said the teenagers were using to “hide from, control and avoid” their feelings; scoff at a student who claimed to be too anxious to return a book to the school library; and challenge a particularly reserved boy who said he had nothing to work on.

Critelli looked at him incredulously. “Dude, you’re failing physics,” Critelli said. “What do you mean you don’t have anything to do?”

“There’s nothing I can do — I’m going to fail,” the student mumbled.

“So you’re just accepting that you’re going to fail?” The boy looked at his hands. “Here’s an idea,” Critelli continued. “You can email your teacher and say, ‘What can I do to improve my grade? What extra work can I do?’ ”

Critelli surveyed his classroom of anxious teenagers. “I’d love to see you advocate for yourselves!”

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A Mountain Valley teenager during equine therapy.CreditSasha Rudensky for The New York Times

Jake is a remarkably minimalist emailer and texter, eschewing exclamation points and emojis in favor of an almost old-fashioned formality. It can be challenging to gauge his moods that way, so I checked in with him regularly by phone in the months after he left Mountain Valley. He usually sounded content when we spoke, an impression confirmed by his parents, who were relieved by the changes they saw in him. In the fall of his senior year, Jake was regularly attending school — on some days he “even enjoyed it,” he told me with a laugh.

While he was careful not to overschedule himself, anxiety still sometimes overtook him. One weekend, he had to leave a Model United Nations conference after he became anxious and his stomach started cramping. “That was really disheartening, but when I struggle now it doesn’t last long, and I can usually get myself out of it pretty quickly,” he said, by talking back to his negative thoughts.

Jake also confessed to some worry about his application to attend U.N.C. He had decided to be transparent with the school about his anxiety disorder, partly because it helped explain his junior-year absences and grades and partly because the months he had spent challenging his beliefs and ideas at Mountain Valley perfectly fit the application essay prompt: Reflect on a time when you challenged a belief or idea.

In 650 thoughtful and sometimes uncharacteristically dramatic words, Jake explained that in middle school he had “aced the tests and seemed to many as the bright future of the American ideal.” But then came high school and fear of failure, the debilitating worry that he might not be good enough. He explained that going to treatment helped him change his perspective on learning and life. “Just being able to type this very essay would have been impossible months ago due to my fear of judgment,” he wrote. “College is the next step in my journey to find a true sense of self, both academically and personally. The future has reopened its doors.”

The doors had not reopened quite as wide for Jillian, whom I visited on an oppressively humid spring afternoon in Florida. It was a school day, but Jillian wasn’t at school. Instead, she was on the screened-in back patio of the townhouse where she lives with her mother, Allison. A talented artist, Jillian loves theater and special-effects makeup design, and she was hard at work on an outfit for a “Walking Dead” costume contest at a local car dealership.

While she painted her costume to make it appear blood-soaked, we half-watched an episode of the Netflix series “13 Reasons Why” on her laptop. Jillian told me she could relate to many of the series’s themes, including cyberbullying. In middle school, she made a profile page on ASKfm, a social-networking site favored at the time by mean girls and their unsuspecting prey. Jillian was quickly targeted. “I’d get 30 mean questions or messages a day,” she said. “Most of them were like, ‘Just kill yourself.’ ”

Nothing like that happened at the small private high school Jillian attended after leaving Mountain Valley. Though the school is known for its flexibility and willingness to work with nontraditional students, Jillian still struggled to feel comfortable there. She didn’t want to open up and be known as “the anxious girl.” There were other students at school who had severe anxiety and depression — “It’s like the flu broke out here with anxious kids this year,” the headmaster told me — but Jillian didn’t feel comfortable hanging out with them, either. Several had yet to go to treatment, and “I don’t want to go backward,” she told me. But the end result, unsurprisingly, was that most students never got to know Jillian.

Her longtime pattern of missing school began again. She had the tools to challenge her anxious thoughts, but using them every day proved exhausting. “There’s feeling a weight on your chest, and there’s the feeling of 16 people sitting on top of each other on your chest,” she said. “As soon as I’d wake up, it was absolute dread.”

Needing to get to her job 40 minutes away each morning, Allison, who had sold her previous house in order to afford Mountain Valley, had little time to coax Jillian out of bed. They argued constantly. Jillian thought her mother — who was severely depressed during a year when Jillian was younger and especially needed support — could be insensitive. Allison struggled with when (and how hard) to push her daughter. She knew Jillian had a serious disorder, but she also knew it wouldn’t get better by letting her hide out in her room. Allison also couldn’t be sure when Jillian was genuinely paralyzed by anxiety and when she was “manipulating me to get out of doing whatever she didn’t feel like doing,” she said.

“The million-dollar question of raising an anxious child is: When is pushing her going to help because she has to face her fears, and when is it going to make the situation worse and she’s going to have a panic attack?” Allison told me. “I feel like I made the wrong decision many times, and it destroyed my confidence as a mother.”

Allison sometimes wondered how her own anxiety issues might have genetically predisposed her daughter to anxiety. Allison had done enough Google searches to know that anxious teenagers tend to come from anxious parents. Research points to hereditary genes that predispose children to an anxiety disorder, and studies have found that an overbearing or anxious parenting style can induce anxiety and risk-aversion in kids. In the parents’ workshop I attended in Oregon, Ashworth, the therapist, spent a lot of time urging family members to work on their own anxiety issues.

He also cautioned parents not to accommodate their children’s avoidance strategies. Families of children with OCD will routinely open doors for them, cook only the two or three specific foods they’ve agreed to eat and avoid saying certain words or sounds. Families of socially anxious kids will let them stay in the car while they go shopping, order for them at restaurants and communicate with a teacher because they’re afraid to. “So many teens have lost the ability to tolerate distress and uncertainty, and a big reason for that is the way we parent them,” Ashworth said.

While Ashworth can be blunt, he is also disarming and funny, with a self-deprecating sense of humor that appeals to both parents and their cynical children. Like many therapists who work with anxious teenagers, he tries to model a “let’s not take life — and ourselves — too seriously” approach. He also has an almost endless empathy for the challenges that these teenagers and their families face. He knows, for example, that raising a severely anxious child can feel counterintuitive. How, for example, do you set and enforce limits with an anxious teenager? If you send him to his room, “you’ve just made his day,” Ashworth told the parents in his workshop, who nodded knowingly.

Though Jillian had returned from Mountain Valley a more confident person with a nuanced understanding of her issues (and with her emetophobia largely under control), treatment didn’t solve her school struggles. As she fell further behind, her morning battles with her mother became increasingly untenable. In consultation with the school, Allison agreed to let Jillian drop out and study for the G.E.D. But Allison wasn’t happy about it; she considered it a momentary concession. “We basically said, ‘O.K., anxiety, you win.’ ”

Jillian was relieved never to have to set foot in another high school. “I’m just a lot more relaxed now,” she told me in her messy bedroom, where the walls were adorned with “Star Wars” posters and the bookshelf overflowed with young-adult fiction and sci-fi, as well as a worn copy of “Chicken Soup for the Teenage Soul.” Near her bed were two prescription bottles — one for Prozac and another for Klonopin, a benzodiazepine tranquilizer. Jillian had been prescribed a number of drug combinations over the years, and while none were panaceas, she believed she would be “a lot worse if I wasn’t taking them.”

Though she spoke to a therapist once or twice a week online, Jillian otherwise ignored the structured daily schedule — including yoga, studying and cleaning her room — that she had agreed to with her mother. Jillian told me she often felt lonely at home, and she spent much of her days texting friends from around the country, some of whom she met at “Star Wars” conventions or on social media.

At the same time, Jillian was trying to make new friends. I watched her joke with fellow contestants at the costume contest (where she walked away with a $250 prize), and she was practically a social butterfly at a film event she attended with her mother. Bored with our company after the screening, Jillian spotted two teenagers talking to each other in a corner.

“O.K., I’m going to go mingle,” she announced.

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A Mountain Valley teenager talking to a passer-by during exposure therapy. Credit Sasha Rudensky for The New York Times

On a busy weekday morning last May, a new crop of Mountain Valley residents were discovering that a key component of their treatment would involve repeatedly making fools of themselves. On the Dartmouth College campus, eight teenagers wore hand-painted white T-shirts that read “Ask Me About My Anxiety” and “I Have OCD.” They were encouraged by the therapy team to come up with scenarios that would make them uncomfortable. One teenager considered approaching random guys on campus and saying, “You must be a Dartmouth football player.” Later that afternoon, a second group of teenagers arrived. One feigned a panic attack at Starbucks. Another ordered nonsensically at a restaurant.

“What do we need to do to make your anxiety higher?” McCallie-Steller, the therapist, asked several teenagers as they prepared for their morning of exposure therapy. First developed in the 1950s, the technique is an essential component of cognitive-behavioral therapy (CBT) for anxiety, which a vast majority of researchers and clinicians believe is the most effective treatment for a range of anxiety disorders. In a large 2008 study of anxious youth  published in The New England Journal of Medicine, more improved using CBT (60 percent) than the antidepressant Zoloft (55 percent), though the most effective therapy (81 percent) was a combination of the two.

But while exposure therapy has been proved highly effective, few teenagers receive it. “We’re much more likely to medicate kids than to give them therapy,” says Stephen Whiteside, director of the Child and Adolescent Anxiety Disorders Program at the Mayo Clinic. “And when we do give them therapy, it’s unlikely to be exposure. With a few exceptions, we’re not treating people with what actually works best.”

Part of the reason is that exposure work is hard. Anxious people aren’t typically eager to feel more anxious. “It’s also uncomfortable for many therapists,” Whiteside told me. “Most people go into therapy or psychology to help people, but with exposure therapy you’re actually helping them feel uncomfortable. It’s not much fun for anybody. It’s much easier to sit in a therapist’s office and talk about feelings.”

Researchers are trying to better understand how exposure works in the brain and to fine-tune its application for anxiety treatment. At U.C.L.A., scientists at the school’s Anxiety and Depression Research Center discovered that the more anxious a person feels going into an exposure exercise, and the more surprised he or she is by the result, the more effective it is at competing with an original negative association or traumatic memory. (That’s why McCallie-Steller did her best to ramp up the teenagers’ anxiety before they began their exposure work.) Other researchers are focused on virtual-reality-aided exposure therapy, which allows people to encounter the sources of their anxiety in a therapist’s office.

For two Mountain Valley 14-year-olds on the main quad at Dartmouth, the sources of their distress were numerous. One, a brown-haired boy who embarrassed easily, suffered from a dispiriting combination of social anxiety, OCD, binge-eating and depression. It was a lot to work on in three months, and he was often overwhelmed by the magnitude of the project. On this day, he had agreed to tackle his social anxiety by sitting next to a stranger on a park bench and striking up a conversation.

Earlier, another Mountain Valley teenager took part in a similar exercise, during which the stranger opened up about his own struggles with anxiety. The teenagers were sometimes surprised that others could relate to their issues. As one girl handed out fliers about anxiety on campus, she sometimes asked people, “Can I tell you about anxiety?” More than a few students — including one who looked as if he might actually be a Dartmouth football player — responded with some version of “Trust me, I know allabout it.”

The brown-haired boy was highly anxious about his exposure. He bombarded the therapist, Bryan Randolph, with questions in a seeming attempt to run out the clock until they had to return to Mountain Valley. “Can I just sit on the bench for a minute?” he asked Randolph. “And can I sit down and then start talking? I mean, do I need to ask, ‘Do you mind if I sit there?’ It’s weird to just sit there, have a conversation, then get up and come running back to a group of people.”

“Even better — let’s make it weird,” Randolph told him.

The boy shook his head. “Maybe the guy’s on break and doesn’t want to be bothered.”

“Maybe,” Randolph said. “He might hate you. He might get real mad at you.”

“That’s terrifying,” the teenager confessed. “And what if we’re so close on the bench that we’re touching?”

“That would be awkward,” Randolph said with a half-smile.

The boy craned his neck to get a better look at the man. “Is he sitting in the middle of the bench?”

“I don’t know — he might be,” Randolph told him. “But are you going to ‘what if’ this to death, or are you going to do it?”

He eventually shuffled off toward the stranger, allowing Randolph to turn his attention to the other 14-year-old, Thomas, who stood sheepishly on a nearby corner holding his sign: “I’ve Been Bullied. Ask Me.” The “Ask Me” was hard to make out, because Thomas had also included many of the insults peers have hurled at him over the years, including “B*tch,” “F*ggot,” “Ur Fat” and “Kill Yourself.” Holding the sign on a busy corner had been Thomas’s idea; he thought it might ratchet up his anxiety and force him to interact with strangers, while having the potential added benefit of educating people about bullying.

Randolph and I watched dozens of students walk by, some giving Thomas’s sign a glance but most never slowing their stride. He had been bullied for years, and now he was being ignored. I felt anxious just looking at him.

Eventually, an attractive couple in their mid-20s stopped to read the sign. They smiled, Thomas beamed and after a minute or two of conversation they all hugged. “Oh, my God, that was the greatest,” Thomas announced upon his return.

I asked him what they’d talked about. “The muscular dude said he’s been bullied, too, in middle school, and that bullies get nowhere in life,” Thomas told us. “Then the girl said, ‘You’re really brave. Can I give you a hug?’ ”

“That’s not what you were expecting, huh?” Randolph said. “Instead of being mean to you, people actually treated you with compassion.”

“Yeah, it was awesome,” he said. “I feel so good!”

The brown-haired boy, meanwhile, returned from his brief visit to the bench: “It was sooooo awkward,” he reported. “The guy just kept texting. He was probably like, Why is this kid asking me questions?”

“And what if he was?” Randolph asked him. “You’re not responsible for what he’s thinking.”

The boy appeared to consider Randolph’s point as they made their way back to the van that would return them to Mountain Valley. Sometimes, Randolph told the boys, “exactly what you think will happen happens. Other times, the exact opposite of what you think will happen happens. Either way, it’s all manageable.”

The subject line of Jake’s email to me last winter read simply, “College Results.” I opened it: “Hey Benoit, I just wanted to tell you that I was accepted to U.N.C. Chapel Hill. Jake.” I emailed back to say that he could stand to sound a little bit more excited, to which he replied, “Trust me, I’m pretty excited!”

Last month, I visited him during his fourth week of college classes. It was a Sunday, and Jake met me outside his dorm wearing khaki shorts and a Carolina Panthers jersey. He looked happier than I’d ever seen him. “Let’s walk,” he said, leading me on a tour of campus and nearby Chapel Hill, where he went record shopping (he left with a Parquet Courts album) and played touch football with a few of his friends.

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Teenagers at the chicken coop at Mountain Valley.CreditSasha Rudensky for The New York Times

Since leaving Mountain Valley, Jake had prioritized his social life. “The health of my relationships with people is just as important as academics,” he told me on a bench overlooking the main quad. He had said something similar at Mountain Valley, but back then it sounded theoretical, aspirational. It felt true now. He had made new friends on campus and was keeping up with old ones from home — and some of his peers from Mountain Valley — via text and Snapchat, the only social-media platform he regularly uses these days. “My junior year, when things got really bad, I told myself that I didn’t need to hang out with my friends a lot, that all that really mattered was how well I did at school,” he said. “I don’t think like that anymore.”

That’s not to say that Jake doesn’t study. He does — usually days before he needs to. “Procrastination isn’t a good idea for me,” he said. But he was actually enjoying several of his college classes, especially Intro to Ethics, for which he was reading Plato’s “Republic.”

Jake had experienced only one intense bout of anxiety at U.N.C. For his info sciences course, he turned in an assignment online but realized days later that there had been a technical glitch and it hadn’t gone through. He said he felt “a sudden burst of anxiety” — his chest tightened, and adrenaline coursed through his body. What had he done? He sent a panicked email to his professor and told a friend who also has anxiety issues that he was “freaking out.” Then he took a nap, which had long been one of his coping strategies. When he awoke, the professor had emailed saying it wasn’t a big deal. “That ended that crisis,” Jake told me.

For the most part, Jake felt he was managing his anxiety. Over the summer, he met twice with Jonathan Abramowitz, a psychology professor who leads the university’s anxiety and stress lab, but Jake had put off finding a regular therapist for the school year. His parents kept bugging him about it. “I just haven’t felt like I need it here,” Jake told me. But then, a few beats later, he added: “I know I need to stop making excuses and just do it.”

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Carrying apples to the pasture to feed the cows on Mountain Valley’s campus.CreditSasha Rudensky for The New York Times

I was curious how much of Jake’s newfound contentment had to do with being at U.N.C., with getting into his dream school. After all, a major component of his treatment at Mountain Valley was learning to accept that his value didn’t depend solely on academic achievement. How would he have reacted if his application was one of the 74 percent that U.N.C. rejected last year?

It was clear that Jake had thought about the question. “I would have been disappointed, but I really think I would have been O.K.,” he told me. “There are other schools in the world where I would have been happy. I definitely wouldn’t have believed that a couple years ago, but a lot’s changed.”

Before walking back to his dorm, where Jake’s friends were waiting for him, we stopped at the Old Well, a campus landmark where legend has it that students who drink from it on the first day of classes will get straight A’s that semester. The old Jake might have been first in line. But the new Jake? He hadn’t bothered to show up.

Alarmed, Jake’s parents sent him to his primary-care physician, who prescribed Prozac, an antidepressant often given to anxious teenagers. It was the first of many medications that Jake, who asked that his last name not be used, would try over the next year. But none seemed to work — and some made a bad situation worse. An increase in dosage made Jake “much more excited, acting strangely and almost manic,” his father wrote in a journal in the fall of 2015. A few weeks later, Jake locked himself in a bathroom at home and tried to drown himself in the bathtub.

He was hospitalized for four days, but soon after he returned home, he started hiding out in his room again. He cried, slept, argued with his parents about going to school and mindlessly surfed the internet on his phone. The more school he missed, the more anxious he felt about missing school. And the more anxious he felt, the more hopeless and depressed he became. He had long wanted to go to the University of North Carolina at Chapel Hill, but now that felt like wishful thinking.

Not every day was bad. During spring break in 2016, Jake’s father wrote: “Jake was relaxed and his old sarcastic, personable, witty self.” A week later, though, Jake couldn’t get through a school day without texting his mother to pick him up or hiding out in the nurse’s office. At home, Jake threatened suicide again. His younger siblings were terrified. “It was the depth of hell,” his mother told me.

That summer, after two more hospitalizations, Jake’s desperate parents sent him to Mountain Valley in New Hampshire, a residential treatment facility and one of a growing number of programs for acutely anxious teenagers. Over the last decade, anxiety has overtaken depression as the most common reason college students seek counseling services. In its annual survey of students, the American College Health Association found a significant increase — to 62 percent in 2016 from 50 percent in 2011 — of undergraduates reporting “overwhelming anxiety” in the previous year. Surveys that look at symptoms related to anxiety are also telling. In 1985, the Higher Education Research Institute at U.C.L.A. began asking incoming college freshmen if they “felt overwhelmed by all I had to do” during the previous year. In 1985, 18 percent said they did. By 2010, that number had increased to 29 percent. Last year, it surged to 41 percent.

Those numbers — combined with a doubling of hospital admissions for suicidal teenagers over the last 10 years, with the highest rates occurring soon after they return to school each fall — come as little surprise to high school administrators across the country, who increasingly report a glut of anxious, overwhelmed students. While it’s difficult to tease apart how much of the apparent spike in anxiety is related to an increase in awareness and diagnosis of the disorder, many of those who work with young people suspect that what they’re seeing can’t easily be explained away. “We’ve always had kids who didn’t want to come in the door or who were worried about things,” says Laurie Farkas, who was until recently director of student services for the Northampton public schools in Massachusetts. “But there’s just been a steady increase of severely anxious students.”

For the teenagers who arrive at Mountain Valley, a nonprofit program that costs $910 a day and offers some need-based assistance, the center is usually a last resort after conventional therapy and medications fail. The young people I met there suffered from a range of anxiety disorders, including social anxiety, separation anxiety, post-traumatic stress disorder and obsessive-compulsive disorder. (Though OCD and PTSD are considered anxiety disorders at Mountain Valley and other treatment centers, they were moved into separate categories in the most recent edition of the Diagnostic and Statistical Manual of Mental Disorders.)

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Sharon McCallie-Steller, a therapist, during a counseling session at the Mountain Valley residential program in New Hampshire.CreditSasha Rudensky for The New York Times

Mountain Valley teenagers spend a lot of time analyzing — and learning to talk back to — their anxious thoughts. During one group session in the summer of 2016 in a sunlit renovated barn with couches, a therapist named Sharon McCallie-Steller instructed everyone to write down three negative beliefs about themselves. That’s an easy exercise for anxious young people (“Only three?” one girl quipped), but McCallie-Steller complicated the assignment by requiring the teenagers to come up with a “strong and powerful response” to each negative thought.

She asked for volunteers. First, residents would share their negative beliefs and rebuttals with the group. Then others would act those out, culminating in a kind of public performance of private teenage insecurity.

Jake raised his hand. By then, he was in his third month at Mountain Valley, and he looked considerably less anxious than several of the newcomers, including one who sat slumped on a couch with his head in his hands. “I’m free to play the part of terrible, evil thoughts for anyone who needs them,” Jake said with a smile. He had already spent weeks challenging his own thinking, which often persuaded him that if he failed a single quiz at school, “then I’ll get a bad grade in the class, I won’t get into the college I want, I won’t get a good job and I’ll be a total failure.”

At Mountain Valley, Jake learned mindfulness techniques, took part in art therapy and equine therapy and, most important, engaged in exposure therapy, a treatment that incrementally exposes people to what they fear. The therapists had quickly figured out that Jake was afraid of failure above all else, so they devised a number of exercises to help him learn to tolerate distress and imperfection. On a group outing to nearby Dartmouth College, for example, Jake’s therapist suggested he strike up conversations with strangers and tell them he didn’t have the grades to get into the school. The college application process was a source of particular anxiety for Jake, and the hope was that he would learn that he could talk about college without shutting down — and that his value as a person didn’t depend on where he went to school.

Though two months in rural New Hampshire hadn’t cured Jake of anxiety, he had made significant progress, and the therapy team was optimistic about his return home for his senior year. Until then, Jake wanted to help other Mountain Valley teenagers face their fears.

Among them was Jillian, a 16-year-old who, when she wasn’t overwhelmed with anxiety, came across as remarkably poised and adultlike, the kind of teenager you find yourself talking to as if she were a graduate student in psychology. Jillian, who also asked that her last name not be used, came to Mountain Valley after two years of only intermittently going to school. She suffered from social anxiety (made worse by cyberbullying from classmates) and emetophobia, a fear of vomit that can be so debilitating that people will sometimes restrict what they eat and refuse to leave the house, lest they encounter someone with a stomach flu.

Jillian listened as Jake and other peers — who, in reality, liked her very much — voiced her insecurities: “I can’t believe how insignificant Jillian is.” “I mean, for the first three weeks, I thought her name was Susan.” “If she left tomorrow, maybe we wouldn’t even miss her.”

At the last one, Jillian’s shoulders caved, and her eyes watered. “I don’t want to do this,” she said, looking meekly at McCallie-Steller.

“If it’s too much, you can stop,” the therapist said, but Jillian considered the offer only long enough to reject it. She straightened her back. “No, I feel like I need to do this,” she announced. “I have a week and a half left. If I can’t get through something like this here …”

Her voice trailed off, but the implication was clear: The real world would be much more anxiety producing — and much less forgiving.

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Jillian in her room in Florida.CreditSasha Rudensky for The New York Times

Anxiety is the most common mental-health disorder in the United States, affecting nearly one-third of both adolescents and adults, according to the National Institute of Mental Health. But unlike depression, with which it routinely occurs, anxiety is often seen as a less serious problem.

“Anxiety is easy to dismiss or overlook, partially because everyone has it to some degree,” explained Philip Kendall, director of the Child and Adolescent Anxiety Disorders Clinic at Temple University in Philadelphia. It has an evolutionary purpose, after all; it helps us detect and avoid potentially dangerous situations. Highly anxious people, though, have an overactive fight-or-flight response that perceives threats where there often are none.

But sometimes there are good reasons to feel anxious. For many young people, particularly those raised in abusive families or who live in neighborhoods besieged by poverty or violence, anxiety is a rational reaction to unstable, dangerous circumstances. At the Youth Anxiety Center’s clinic in the Washington Heights neighborhood of Manhattan, which serves mostly poor and working-class Hispanic youth, teenagers would object to the definition of anxiety I heard often at Mountain Valley: “The overestimation of danger and the underestimation of our ability to cope.”

“The fears can be very real for our kids,” explained Carolina Zerrate, the clinic’s medical director. “Oftentimes their neighborhoods are not safe, their streets are not safe and their families can feel unsafe if there’s a history of trauma and abuse.” The contemporary political climate can also feel “incredibly unsafe for the community of kids we serve,” Zerrate adds, explaining that many have undocumented family members.

And yet addressing anxiety is low on the priority list in many economically disadvantaged communities. Kids who “act out” are often labeled defiant or aggressive, while those who keep to themselves — anxiety specialists call them “silent sufferers” — are overlooked or mistaken for being shy. “If you go to a public school in a struggling urban area, teachers will talk about drugs, crime, teen pregnancy, violence,” Kendall says. “When you start to talk about anxiety, they’re like, ‘Oh, those are the kids we like!’ ”

Teenagers raised in more affluent communities might seemingly have less to feel anxious about. But Suniya Luthar, a professor of psychology at Arizona State University who has studied distress and resilience in both well-off and disadvantaged teenagers, has found that privileged youths are among the most emotionally distressed young people in America. “These kids are incredibly anxious and perfectionistic,” she says, but there’s “contempt and scorn for the idea that kids who have it all might be hurting.”

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A resident taking part in equine therapy at Mountain Valley.CreditSasha Rudensky for The New York Times

For many of these young people, the biggest single stressor is that they “never get to the point where they can say, ‘I’ve done enough, and now I can stop,’ ” Luthar says. “There’s always one more activity, one more A.P. class, one more thing to do in order to get into a top college. Kids have a sense that they’re not measuring up. The pressure is relentless and getting worse.”

It’s tempting to blame helicopter parents with their own anxiety issues for that pressure (and therapists who work with teenagers sometimes do), but several anxiety experts pointed to an important shift in the last few years. “Teenagers used to tell me, ‘I just need to get my parents off my back,’ ” recalls Madeline Levine, a founder of Challenge Success, a Stanford University-affiliated nonprofit that works on school reform and student well-being. “Now so many students have internalized the anxiety. The kids at this point are driving themselves crazy.”

Though there are cultural differences in how this kind of anguish manifests, there’s considerable overlap among teenagers from different backgrounds. Many are anxious about school and how friends or teachers perceive them. Some obsess about family conflicts. Teenagers with OCD tend to worry excessively about what foods they should eat, diseases they might contract or whatever happens to be in the news that week. Stephanie Eken, a psychiatrist and the regional medical director for Rogers Behavioral Health, which runs several teenage-anxiety outpatient programs across the country and an inpatient program in Wisconsin, told me that in the last few years she has heard more kids than ever worry about terrorism. “They wonder about whether it’s safe to go to a movie theater,” she said.

When I asked Eken about other common sources of worry among highly anxious kids, she didn’t hesitate: social media. Anxious teenagers from all backgrounds are relentlessly comparing themselves with their peers, she said, and the results are almost uniformly distressing.

Anxious kids certainly existed before Instagram, but many of the parents I spoke to worried that their kids’ digital habits — round-the-clock responding to texts, posting to social media, obsessively following the filtered exploits of peers — were partly to blame for their children’s struggles. To my surprise, anxious teenagers tended to agree. At Mountain Valley, I listened as a college student went on a philosophical rant about his generation’s relationship to social media. “I don’t think we realize how much it’s affecting our moods and personalities,” he said. “Social media is a tool, but it’s become this thing that we can’t live without but that’s making us crazy.”

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A resident meditating during a yoga session at Mountain Valley.CreditSasha Rudensky for The New York Times

In his case, he had little doubt that social media made him more self-conscious. “In high school, I’d constantly be judging my self-worth online,” he told me, recalling his tortured relationship with Facebook. “I would think, Oh, people don’t want to see me on their timeline.”

While smartphones can provoke anxiety, they can also serve as a handy avoidance strategy. At the height of his struggles, Jake spent hours at a time on his phone at home or at school. “It was a way for me not to think about classes and college, not to have to talk to people,” he said. Jake’s parents became so alarmed that they spoke to his psychiatrist about it and took his phone away a few hours each night.

At a workshop for parents last fall at the NW Anxiety Institute in Portland, Ore., Kevin Ashworth, the clinical director, warned them of the “illusion of control and certainty” that smartphones offer anxious young people desperate to manage their environments. “Teens will go places if they feel like they know everything that will happen, if they know everyone who will be there, if they can see who’s checked in online,” Ashworth told the parents. “But life doesn’t always come with that kind of certainty, and they’re never practicing the skill of rolling with the punches, of walking into an unknown or awkward social situation and learning that they can survive it.”

Jean Twenge, a professor of psychology at San Diego State University who researches adolescent mental health and psychological differences among generations, used to be skeptical of those who sounded an alarm about teenage internet use. “It seemed like too easy an explanation for negative mental-health outcomes in teens, and there wasn’t much evidence for it,” she told me. She searched for other possible explanations, including economic ones. But the timing of the spike in anxious and depressed teenagers since 2011, which she called one of the sharpest and most significant she has seen, is “all wrong,” she said. “The economy was improving by the time the increase started.”

The more she looked for explanations, the more she kept returning to two seemingly unrelated trend lines — depression in teenagers and smartphone adoption. (There is significantly more data about depression than anxiety.) Since 2011, the trend lines increased at essentially the same rate. In her recent book “iGen,” and in an article in The Atlantic, Twenge highlights a number of studies exploring the connection between social media and unhappiness. “The use of social media and smartphones look culpable for the increase in teen mental-health issues,” she told me. “It’s enough for an arrest — and as we get more data, it might be enough for a conviction.”

Last fall, at a high school near the New Hampshire-Vermont border, I watched Lynn Lyons, a psychotherapist and author, deliver bad news to a packed auditorium of teachers and counselors. “We’re not getting the job done,” she said, pacing the stage at Fall Mountain Regional High School, where she had been asked to lead a professional-development training session about anxiety.

More than a decade ago, the school would have been unlikely to invite her to speak. Anxiety was barely on the radar of most educators back then, according to Denise Pope, another founder of Challenge Success, the Stanford-affiliated nonprofit. Pope remembers facing skepticism when she sounded the alarm about growing anxiety among teenagers. “We don’t have to convince them anymore,” she told me. “Schools are coming to us, eager for help.”

A gregarious speaker, Lyons kept her audience entertained by calling anxiety “the cult leader” — for its ability to convince people of falsehoods about themselves — and telling funny stories about overinvolved parents. But her main point was clear: In a seemingly well-meaning effort to help kids avoid what makes them anxious, administrators actually make anxiety worse. “Anxiety is all about the avoidance of uncertainty and discomfort,” Lyons explained. “When we play along, we don’t help kids learn to cope or problem-solve in the face of unexpected events.”

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Kids hanging out in the lounge after lunch at Mountain Valley.CreditSasha Rudensky for The New York Times

She pointed to the increasing use of “504 plans,” a popular educational tool that allows for academic accommodations for students with physical or mental disabilities. Though 504 plans for anxiety vary by student, a typical one might allow a teenager to take more time on homework and tests, enter the school through a back door — to avoid the chaos of the main entrance — and leave a classroom when feeling anxious.

Lyons believes in the necessity of 504 plans, and she is in agreement with many of the recommendations of Challenge Success, including later school start times, less homework and more project-based learning. But Lyons worries that too many 504 plans are “avoidance-based and teach zero skills.” She gave the example of a plan that allows a student to leave a classroom anytime he feels overwhelmed. Often, a teenager “can go wherever he wants and stay there for as long as he thinks he needs,” she said. Instead, she argued, a school should have a policy in place for the student to seek out a guidance counselor or nurse and do some role-playing that helps the student “externalize his worry,” similar to how Mountain Valley teenagers are taught to observe their thinking and talk back to it. Then the student should return to his regular classroom as soon as possible, Lyons said.

“If anxiety could talk, it would say, ‘You know, let’s just get out of here. We don’t have to do this!’ ” Lyons said from the stage. “But in order to retrain the brain, in order to create that message that says that even though I’m uncomfortable I can do this, we need to stop treating these anxious kids like they’re so frail, like they can’t handle things.”

Lyons sees a connection between how some schools deal with anxious students and what she worries is a generation of young people increasingly insistent on safe spaces — and who believe their feelings should be protected at all costs. “Kids are being given some really dangerous messages these days about the fact that they can’t handle being triggered, that they shouldn’t have to bear witness to anything that makes them uncomfortable and that their external environments should bend to and accommodate their needs,” she told me.

Among many teachers and administrators I spoke to, one word — “resiliency” — kept coming up. More and more students struggle to recover from minor setbacks and aren’t “equipped to problem-solve or advocate for themselves effectively,” a school counselor in suburban Oregon told me. In the last few years, the counselor said, she has watched in astonishment as more students struggle with anxiety — and as more of those “stop coming to school, because they just can’t.”

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A Mountain Valley resident doing art therapy.CreditSasha Rudensky for The New York Times

Some schools have taken drastic measures to accommodate what one administrator called “our more fragile students.” At Roxbury High School in Roxbury Township, N.J., there are two dedicated classrooms for anxious teenagers, including one next to a mural of Edvard Munch’s painting “The Scream.” These students typically avoid the mammoth school cafeteria in favor of eating lunch in one of the classrooms, as they did on the day of my visit last May. They had just finished gym class, an anxiety-producing event for some even as the school did all it could to reimagine the concept. Music blasted throughout the gym as the teenagers halfheartedly played something vaguely approximating a game of volleyball. The ball was allowed to bounce once before being struck — not that anyone was keeping score.

I couldn’t help wondering what Lyons, and other therapists I spoke to who worry that schools inadvertently worsen anxiety, would think of this approach. Some of the programs’ teenagers hoped to go to college, where no special classrooms would await them. How was this preparing them for that?

“Some will say that this feeds the monster,” concedes Patricia Hovey, director of special services at Roxbury High. “But you’ve got to start where the kids are, not where you are or where you want them to be. We’ve got to get them in the building. Many of our students simply don’t come to school if they have to spend all day in” general-education classes. Once the students are in school, Hovey explained, staff members can help them build the confidence and skills to eventually transition to Roxbury’s regular classes — and stand a chance at navigating college or a job once they graduate.

Even with the promise of a special classroom, getting anxious kids to Roxbury High each morning demands a herculean effort from the program’s teachers and therapists. During my visit, I watched them text and call several no-show students in an effort to coax them out of bed. They also regularly communicate with parents, talking them through what to say to a teenager who refuses to leave his room. Paul Critelli, one of the program’s teachers, told me that many parents feel overwhelmed trying to get two or three kids ready for school each morning, and that their instinct is often to “sacrifice the anxious kid” in order to avoid morning hysterics and keep the family train running on time.

Mostly, though, Critelli wants to talk to the anxious students. “What’s the issue today?” I heard him ask during a phone call with a sophomore boy, who had missed his scheduled bus and was presumably speaking to Critelli from underneath his sheets. The call was a “Hail Mary,” as Critelli put it, because while he suspects that the boy sleeps with the phone “right next to his face,” he rarely responds when he’s feeling anxious. “I appreciate you picking up — you don’t normally do that,” Critelli told him, mixing in positive affirmation with a call to action. The school would be sending another bus, and Critelli expected him to be on it.

Critelli looked for any opportunity to push students out of their comfort zones. During an informal study period after lunch, I watched him confiscate cellphones he said the teenagers were using to “hide from, control and avoid” their feelings; scoff at a student who claimed to be too anxious to return a book to the school library; and challenge a particularly reserved boy who said he had nothing to work on.

Critelli looked at him incredulously. “Dude, you’re failing physics,” Critelli said. “What do you mean you don’t have anything to do?”

“There’s nothing I can do — I’m going to fail,” the student mumbled.

“So you’re just accepting that you’re going to fail?” The boy looked at his hands. “Here’s an idea,” Critelli continued. “You can email your teacher and say, ‘What can I do to improve my grade? What extra work can I do?’ ”

Critelli surveyed his classroom of anxious teenagers. “I’d love to see you advocate for yourselves!”

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A Mountain Valley teenager during equine therapy.CreditSasha Rudensky for The New York Times

Jake is a remarkably minimalist emailer and texter, eschewing exclamation points and emojis in favor of an almost old-fashioned formality. It can be challenging to gauge his moods that way, so I checked in with him regularly by phone in the months after he left Mountain Valley. He usually sounded content when we spoke, an impression confirmed by his parents, who were relieved by the changes they saw in him. In the fall of his senior year, Jake was regularly attending school — on some days he “even enjoyed it,” he told me with a laugh.

While he was careful not to overschedule himself, anxiety still sometimes overtook him. One weekend, he had to leave a Model United Nations conference after he became anxious and his stomach started cramping. “That was really disheartening, but when I struggle now it doesn’t last long, and I can usually get myself out of it pretty quickly,” he said, by talking back to his negative thoughts.

Jake also confessed to some worry about his application to attend U.N.C. He had decided to be transparent with the school about his anxiety disorder, partly because it helped explain his junior-year absences and grades and partly because the months he had spent challenging his beliefs and ideas at Mountain Valley perfectly fit the application essay prompt: Reflect on a time when you challenged a belief or idea.

In 650 thoughtful and sometimes uncharacteristically dramatic words, Jake explained that in middle school he had “aced the tests and seemed to many as the bright future of the American ideal.” But then came high school and fear of failure, the debilitating worry that he might not be good enough. He explained that going to treatment helped him change his perspective on learning and life. “Just being able to type this very essay would have been impossible months ago due to my fear of judgment,” he wrote. “College is the next step in my journey to find a true sense of self, both academically and personally. The future has reopened its doors.”

The doors had not reopened quite as wide for Jillian, whom I visited on an oppressively humid spring afternoon in Florida. It was a school day, but Jillian wasn’t at school. Instead, she was on the screened-in back patio of the townhouse where she lives with her mother, Allison. A talented artist, Jillian loves theater and special-effects makeup design, and she was hard at work on an outfit for a “Walking Dead” costume contest at a local car dealership.

While she painted her costume to make it appear blood-soaked, we half-watched an episode of the Netflix series “13 Reasons Why” on her laptop. Jillian told me she could relate to many of the series’s themes, including cyberbullying. In middle school, she made a profile page on ASKfm, a social-networking site favored at the time by mean girls and their unsuspecting prey. Jillian was quickly targeted. “I’d get 30 mean questions or messages a day,” she said. “Most of them were like, ‘Just kill yourself.’ ”

Nothing like that happened at the small private high school Jillian attended after leaving Mountain Valley. Though the school is known for its flexibility and willingness to work with nontraditional students, Jillian still struggled to feel comfortable there. She didn’t want to open up and be known as “the anxious girl.” There were other students at school who had severe anxiety and depression — “It’s like the flu broke out here with anxious kids this year,” the headmaster told me — but Jillian didn’t feel comfortable hanging out with them, either. Several had yet to go to treatment, and “I don’t want to go backward,” she told me. But the end result, unsurprisingly, was that most students never got to know Jillian.

Her longtime pattern of missing school began again. She had the tools to challenge her anxious thoughts, but using them every day proved exhausting. “There’s feeling a weight on your chest, and there’s the feeling of 16 people sitting on top of each other on your chest,” she said. “As soon as I’d wake up, it was absolute dread.”

Needing to get to her job 40 minutes away each morning, Allison, who had sold her previous house in order to afford Mountain Valley, had little time to coax Jillian out of bed. They argued constantly. Jillian thought her mother — who was severely depressed during a year when Jillian was younger and especially needed support — could be insensitive. Allison struggled with when (and how hard) to push her daughter. She knew Jillian had a serious disorder, but she also knew it wouldn’t get better by letting her hide out in her room. Allison also couldn’t be sure when Jillian was genuinely paralyzed by anxiety and when she was “manipulating me to get out of doing whatever she didn’t feel like doing,” she said.

“The million-dollar question of raising an anxious child is: When is pushing her going to help because she has to face her fears, and when is it going to make the situation worse and she’s going to have a panic attack?” Allison told me. “I feel like I made the wrong decision many times, and it destroyed my confidence as a mother.”

Allison sometimes wondered how her own anxiety issues might have genetically predisposed her daughter to anxiety. Allison had done enough Google searches to know that anxious teenagers tend to come from anxious parents. Research points to hereditary genes that predispose children to an anxiety disorder, and studies have found that an overbearing or anxious parenting style can induce anxiety and risk-aversion in kids. In the parents’ workshop I attended in Oregon, Ashworth, the therapist, spent a lot of time urging family members to work on their own anxiety issues.

He also cautioned parents not to accommodate their children’s avoidance strategies. Families of children with OCD will routinely open doors for them, cook only the two or three specific foods they’ve agreed to eat and avoid saying certain words or sounds. Families of socially anxious kids will let them stay in the car while they go shopping, order for them at restaurants and communicate with a teacher because they’re afraid to. “So many teens have lost the ability to tolerate distress and uncertainty, and a big reason for that is the way we parent them,” Ashworth said.

While Ashworth can be blunt, he is also disarming and funny, with a self-deprecating sense of humor that appeals to both parents and their cynical children. Like many therapists who work with anxious teenagers, he tries to model a “let’s not take life — and ourselves — too seriously” approach. He also has an almost endless empathy for the challenges that these teenagers and their families face. He knows, for example, that raising a severely anxious child can feel counterintuitive. How, for example, do you set and enforce limits with an anxious teenager? If you send him to his room, “you’ve just made his day,” Ashworth told the parents in his workshop, who nodded knowingly.

Though Jillian had returned from Mountain Valley a more confident person with a nuanced understanding of her issues (and with her emetophobia largely under control), treatment didn’t solve her school struggles. As she fell further behind, her morning battles with her mother became increasingly untenable. In consultation with the school, Allison agreed to let Jillian drop out and study for the G.E.D. But Allison wasn’t happy about it; she considered it a momentary concession. “We basically said, ‘O.K., anxiety, you win.’ ”

Jillian was relieved never to have to set foot in another high school. “I’m just a lot more relaxed now,” she told me in her messy bedroom, where the walls were adorned with “Star Wars” posters and the bookshelf overflowed with young-adult fiction and sci-fi, as well as a worn copy of “Chicken Soup for the Teenage Soul.” Near her bed were two prescription bottles — one for Prozac and another for Klonopin, a benzodiazepine tranquilizer. Jillian had been prescribed a number of drug combinations over the years, and while none were panaceas, she believed she would be “a lot worse if I wasn’t taking them.”

Though she spoke to a therapist once or twice a week online, Jillian otherwise ignored the structured daily schedule — including yoga, studying and cleaning her room — that she had agreed to with her mother. Jillian told me she often felt lonely at home, and she spent much of her days texting friends from around the country, some of whom she met at “Star Wars” conventions or on social media.

At the same time, Jillian was trying to make new friends. I watched her joke with fellow contestants at the costume contest (where she walked away with a $250 prize), and she was practically a social butterfly at a film event she attended with her mother. Bored with our company after the screening, Jillian spotted two teenagers talking to each other in a corner.

“O.K., I’m going to go mingle,” she announced.

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A Mountain Valley teenager talking to a passer-by during exposure therapy. CreditSasha Rudensky for The New York Times

On a busy weekday morning last May, a new crop of Mountain Valley residents were discovering that a key component of their treatment would involve repeatedly making fools of themselves. On the Dartmouth College campus, eight teenagers wore hand-painted white T-shirts that read “Ask Me About My Anxiety” and “I Have OCD.” They were encouraged by the therapy team to come up with scenarios that would make them uncomfortable. One teenager considered approaching random guys on campus and saying, “You must be a Dartmouth football player.” Later that afternoon, a second group of teenagers arrived. One feigned a panic attack at Starbucks. Another ordered nonsensically at a restaurant.

“What do we need to do to make your anxiety higher?” McCallie-Steller, the therapist, asked several teenagers as they prepared for their morning of exposure therapy. First developed in the 1950s, the technique is an essential component of cognitive-behavioral therapy (CBT) for anxiety, which a vast majority of researchers and clinicians believe is the most effective treatment for a range of anxiety disorders. In a large 2008 study of anxious youth  published in The New England Journal of Medicine, more improved using CBT (60 percent) than the antidepressant Zoloft (55 percent), though the most effective therapy (81 percent) was a combination of the two.

But while exposure therapy has been proved highly effective, few teenagers receive it. “We’re much more likely to medicate kids than to give them therapy,” says Stephen Whiteside, director of the Child and Adolescent Anxiety Disorders Program at the Mayo Clinic. “And when we do give them therapy, it’s unlikely to be exposure. With a few exceptions, we’re not treating people with what actually works best.”

Part of the reason is that exposure work is hard. Anxious people aren’t typically eager to feel more anxious. “It’s also uncomfortable for many therapists,” Whiteside told me. “Most people go into therapy or psychology to help people, but with exposure therapy you’re actually helping them feel uncomfortable. It’s not much fun for anybody. It’s much easier to sit in a therapist’s office and talk about feelings.”

Researchers are trying to better understand how exposure works in the brain and to fine-tune its application for anxiety treatment. At U.C.L.A., scientists at the school’s Anxiety and Depression Research Center discovered that the more anxious a person feels going into an exposure exercise, and the more surprised he or she is by the result, the more effective it is at competing with an original negative association or traumatic memory. (That’s why McCallie-Steller did her best to ramp up the teenagers’ anxiety before they began their exposure work.) Other researchers are focused on virtual-reality-aided exposure therapy, which allows people to encounter the sources of their anxiety in a therapist’s office.

For two Mountain Valley 14-year-olds on the main quad at Dartmouth, the sources of their distress were numerous. One, a brown-haired boy who embarrassed easily, suffered from a dispiriting combination of social anxiety, OCD, binge-eating and depression. It was a lot to work on in three months, and he was often overwhelmed by the magnitude of the project. On this day, he had agreed to tackle his social anxiety by sitting next to a stranger on a park bench and striking up a conversation.

Earlier, another Mountain Valley teenager took part in a similar exercise, during which the stranger opened up about his own struggles with anxiety. The teenagers were sometimes surprised that others could relate to their issues. As one girl handed out fliers about anxiety on campus, she sometimes asked people, “Can I tell you about anxiety?” More than a few students — including one who looked as if he might actually be a Dartmouth football player — responded with some version of “Trust me, I know allabout it.”

The brown-haired boy was highly anxious about his exposure. He bombarded the therapist, Bryan Randolph, with questions in a seeming attempt to run out the clock until they had to return to Mountain Valley. “Can I just sit on the bench for a minute?” he asked Randolph. “And can I sit down and then start talking? I mean, do I need to ask, ‘Do you mind if I sit there?’ It’s weird to just sit there, have a conversation, then get up and come running back to a group of people.”

“Even better — let’s make it weird,” Randolph told him.

The boy shook his head. “Maybe the guy’s on break and doesn’t want to be bothered.”

“Maybe,” Randolph said. “He might hate you. He might get real mad at you.”

“That’s terrifying,” the teenager confessed. “And what if we’re so close on the bench that we’re touching?”

“That would be awkward,” Randolph said with a half-smile.

The boy craned his neck to get a better look at the man. “Is he sitting in the middle of the bench?”

“I don’t know — he might be,” Randolph told him. “But are you going to ‘what if’ this to death, or are you going to do it?”

He eventually shuffled off toward the stranger, allowing Randolph to turn his attention to the other 14-year-old, Thomas, who stood sheepishly on a nearby corner holding his sign: “I’ve Been Bullied. Ask Me.” The “Ask Me” was hard to make out, because Thomas had also included many of the insults peers have hurled at him over the years, including “B*tch,” “F*ggot,” “Ur Fat” and “Kill Yourself.” Holding the sign on a busy corner had been Thomas’s idea; he thought it might ratchet up his anxiety and force him to interact with strangers, while having the potential added benefit of educating people about bullying.

Randolph and I watched dozens of students walk by, some giving Thomas’s sign a glance but most never slowing their stride. He had been bullied for years, and now he was being ignored. I felt anxious just looking at him.

Eventually, an attractive couple in their mid-20s stopped to read the sign. They smiled, Thomas beamed and after a minute or two of conversation they all hugged. “Oh, my God, that was the greatest,” Thomas announced upon his return.

I asked him what they’d talked about. “The muscular dude said he’s been bullied, too, in middle school, and that bullies get nowhere in life,” Thomas told us. “Then the girl said, ‘You’re really brave. Can I give you a hug?’ ”

“That’s not what you were expecting, huh?” Randolph said. “Instead of being mean to you, people actually treated you with compassion.”

“Yeah, it was awesome,” he said. “I feel so good!”

The brown-haired boy, meanwhile, returned from his brief visit to the bench: “It was sooooo awkward,” he reported. “The guy just kept texting. He was probably like, Why is this kid asking me questions?”

“And what if he was?” Randolph asked him. “You’re not responsible for what he’s thinking.”

The boy appeared to consider Randolph’s point as they made their way back to the van that would return them to Mountain Valley. Sometimes, Randolph told the boys, “exactly what you think will happen happens. Other times, the exact opposite of what you think will happen happens. Either way, it’s all manageable.”

The subject line of Jake’s email to me last winter read simply, “College Results.” I opened it: “Hey Benoit, I just wanted to tell you that I was accepted to U.N.C. Chapel Hill. Jake.” I emailed back to say that he could stand to sound a little bit more excited, to which he replied, “Trust me, I’m pretty excited!”

Last month, I visited him during his fourth week of college classes. It was a Sunday, and Jake met me outside his dorm wearing khaki shorts and a Carolina Panthers jersey. He looked happier than I’d ever seen him. “Let’s walk,” he said, leading me on a tour of campus and nearby Chapel Hill, where he went record shopping (he left with a Parquet Courts album) and played touch football with a few of his friends.

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Teenagers at the chicken coop at Mountain Valley.CreditSasha Rudensky for The New York Times

Since leaving Mountain Valley, Jake had prioritized his social life. “The health of my relationships with people is just as important as academics,” he told me on a bench overlooking the main quad. He had said something similar at Mountain Valley, but back then it sounded theoretical, aspirational. It felt true now. He had made new friends on campus and was keeping up with old ones from home — and some of his peers from Mountain Valley — via text and Snapchat, the only social-media platform he regularly uses these days. “My junior year, when things got really bad, I told myself that I didn’t need to hang out with my friends a lot, that all that really mattered was how well I did at school,” he said. “I don’t think like that anymore.”

That’s not to say that Jake doesn’t study. He does — usually days before he needs to. “Procrastination isn’t a good idea for me,” he said. But he was actually enjoying several of his college classes, especially Intro to Ethics, for which he was reading Plato’s “Republic.”

Jake had experienced only one intense bout of anxiety at U.N.C. For his info sciences course, he turned in an assignment online but realized days later that there had been a technical glitch and it hadn’t gone through. He said he felt “a sudden burst of anxiety” — his chest tightened, and adrenaline coursed through his body. What had he done? He sent a panicked email to his professor and told a friend who also has anxiety issues that he was “freaking out.” Then he took a nap, which had long been one of his coping strategies. When he awoke, the professor had emailed saying it wasn’t a big deal. “That ended that crisis,” Jake told me.

For the most part, Jake felt he was managing his anxiety. Over the summer, he met twice with Jonathan Abramowitz, a psychology professor who leads the university’s anxiety and stress lab, but Jake had put off finding a regular therapist for the school year. His parents kept bugging him about it. “I just haven’t felt like I need it here,” Jake told me. But then, a few beats later, he added: “I know I need to stop making excuses and just do it.”

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Carrying apples to the pasture to feed the cows on Mountain Valley’s campus.CreditSasha Rudensky for The New York Times

I was curious how much of Jake’s newfound contentment had to do with being at U.N.C., with getting into his dream school. After all, a major component of his treatment at Mountain Valley was learning to accept that his value didn’t depend solely on academic achievement. How would he have reacted if his application was one of the 74 percent that U.N.C. rejected last year?

It was clear that Jake had thought about the question. “I would have been disappointed, but I really think I would have been O.K.,” he told me. “There are other schools in the world where I would have been happy. I definitely wouldn’t have believed that a couple years ago, but a lot’s changed.”

Before walking back to his dorm, where Jake’s friends were waiting for him, we stopped at the Old Well, a campus landmark where legend has it that students who drink from it on the first day of classes will get straight A’s that semester. The old Jake might have been first in line. But the new Jake? He hadn’t bothered to show up.