He steered into the high school parking lot, clicked off the ignition and scanned the scraps of his recent weeks. Crinkled chip bags on the dashboard. Soda cups at his feet. And on the passenger seat, a rumpled SAT practice book whose owner had been told since fourth grade he was headed to the Ivy League. Pencils up in 20 minutes.

The boy exhaled. Before opening the car door, he recalled recently, he twisted open a capsule of orange powder and arranged it in a neat line on the armrest. He leaned over, closed one nostril and snorted it.

Throughout the parking lot, he said, eight of his friends did the same thing.

The drug was not cocaine or heroin, but Adderall, an amphetamine prescribed for attention deficit hyperactivity disorder that the boy said he and his friends routinely shared to study late into the night, focus during tests and ultimately get the grades worthy of their prestigious high school in an affluent suburb of New York City. The drug did more than just jolt them awake for the 8 a.m. SAT; it gave them a tunnel focus tailor-made for the marathon of tests long known to make or break college applications.

“Everyone in school either has a prescription or has a friend who does,” the boy said.

At high schools across the United States, pressure over grades and competition for college admissions are encouraging students to abuse prescription stimulants, according to interviews with students, parents and doctors. Pills that have been a staple in some college and graduate school circles are going from rare to routine in many academically competitive high schools, where teenagers say they get them from friends, buy them from student dealers or fake symptoms to their parents and doctors to get prescriptions.

Of the more than 200 students, school officials, parents and others contacted for this article, about 40 agreed to share their experiences. Most students spoke on the condition that they be identified by only a first or middle name, or not at all, out of concern for their college prospects or their school systems’ reputations — and their own.

“It’s throughout all the private schools here,” said DeAnsin Parker, a New York psychologist who treats many adolescents from affluent neighborhoods like the Upper East Side. “It’s not as if there is one school where this is the culture. This is the culture.”

Observed Gary Boggs, a special agent for the Drug Enforcement Administration, “We’re seeing it all across the United States.”

The D.E.A. lists prescription stimulants like Adderall and Vyvanse (amphetamines) and Ritalin and Focalin (methylphenidates) as Class 2 controlled substances — the same as cocaine and morphine — because they rank among the most addictive substances that have a medical use. (By comparison, the long-abused anti-anxiety drug Valium is in the lower Class 4.) So they carry high legal risks, too, as few teenagers appreciate that merely giving a friend an Adderall or Vyvanse pill is the same as selling it and can be prosecuted as a felony.

While these medicines tend to calm people with A.D.H.D., those without the disorder find that just one pill can jolt them with the energy and focus to push through all-night homework binges and stay awake during exams afterward. “It’s like it does your work for you,” said William, a recent graduate of the Birch Wathen Lenox School on the Upper East Side of Manhattan.

But abuse of prescription stimulants can lead to depression and mood swings (from sleep deprivation), heart irregularities and acute exhaustion or psychosis during withdrawal, doctors say. Little is known about the long-term effects of abuse of stimulants among the young. Drug counselors say that for some teenagers, the pills eventually become an entry to the abuse of painkillers and sleep aids.

“Once you break the seal on using pills, or any of that stuff, it’s not scary anymore — especially when you’re getting A’s,” said the boy who snorted Adderall in the parking lot. He spoke from the couch of his drug counselor, detailing how he later became addicted to the painkiller Percocet and eventually heroin.

Paul L. Hokemeyer, a family therapist at Caron Treatment Centers in Manhattan, said: “Children have prefrontal cortexes that are not fully developed, and we’re changing the chemistry of the brain. That’s what these drugs do. It’s one thing if you have a real deficiency — the medicine is really important to those people — but not if your deficiency is not getting into Brown.”

The number of prescriptions for A.D.H.D. medications dispensed for young people ages 10 to 19 has risen 26 percent since 2007, to almost 21 million yearly, according to IMS Health, a health care information company — a number that experts estimate corresponds to more than two million individuals. But there is no reliable research on how many high school students take stimulants as a study aid. Doctors and teenagers from more than 15 schools across the nation with high academic standards estimated that the portion of students who do so ranges from 15 percent to 40 percent.

“They’re the A students, sometimes the B students, who are trying to get good grades,” said one senior at Lower Merion High School in Ardmore, a Philadelphia suburb, who said he makes hundreds of dollars a week selling prescription drugs, usually priced at $5 to $20 per pill, to classmates as young as freshmen. “They’re the quote-unquote good kids, basically.”

The trend was driven home last month to Nan Radulovic, a social worker in Santa Monica, Calif. Within a few days, she said, an 11th grader, a ninth grader and an eighth grader asked for prescriptions for Adderall solely for better grades. From one girl, she recalled, it was not quite a request.

“If you don’t give me the prescription,” Ms. Radulovic said the girl told her, “I’ll just get it from kids at school.”

Keeping Everyone Happy

Madeleine surveyed her schedule of five Advanced Placement classes, field hockey and several other extracurricular activities and knew she could not handle it all. The first physics test of the year — inclines, friction, drag — loomed ominously over her college prospects. A star senior at her Roman Catholic school in Bethesda, Md., Madeleine knew a friend whose grades had gone from B’s to A’s after being prescribed Ritalin, so she asked her for a pill.

She got a 95. Thereafter, Madeleine recalled, she got Adderall and Vyvanse capsules the rest of the year from various classmates — not in exchange for money, she said, but for tutoring them in calculus or proofreading their English papers.

“Can I get a drink of water?” Madeleine said she would ask the teacher in one class, before excusing herself and heading to the water fountain. Making sure no one was watching, she would remove a 40-milligram Vyvanse capsule from her purse and swallow it. After 30 minutes, the buzz began, she said: laser focus, instant recall and the fortitude to crush any test in her path.

“People would have never looked at me and thought I used drugs like that — I wasn’t that kid,” said Madeleine, who has just completed her freshman year at an Ivy League college and continues to use stimulants occasionally. “It wasn’t that hard of a decision. Do I want only four hours of sleep and be a mess, and then underperform on the test and then in field hockey? Or make the teachers happy and the coach happy and get good grades, get into a good college and make my parents happy?”

Madeleine estimated that one-third of her classmates at her small school, most of whom she knew well, used stimulants without a prescription to boost their scholastic performance. Many students across the United States made similar estimates for their schools, all of them emphasizing that the drugs were used not to get high, but mostly by conscientious students to work harder and meet ever-rising academic expectations.

These estimates can be neither confirmed nor refuted because little data captures this specific type of drug misuse. A respected annual survey financed by the National Institute on Drug Abuse, “Monitoring the Future,” reports that abuse of prescription amphetamines by 10th and 12th graders nationally has actually dipped from the 1990s and is remaining relatively steady at about 10 percent.

However, some experts note that the survey does not focus on the demographic where they believe such abuse is rising steadily — students at high-pressure high schools — and also that many teenagers barely know that what they often call “study drugs” are in fact illegal amphetamines.

“Isn’t it just like a vitamin?” asked one high school junior from Eastchester, a suburb of New York.

Liz Jorgensen, a licensed addiction specialist who runs Insight Counseling in Ridgefield, Conn., said her small center had treated “at least 50 or 60” high school students from southern Connecticut this school year alone who had abused prescription stimulants for academics. Ms. Jorgensen said some of those teenagers landed in rehab directly from the stimulants or, more often, grew comfortable with prescription drugs in general and began abusing prescription painkillers like OxyContin.

A spokesman for Shire, which manufactures Vyvanse and Adderall’s extended-release capsules, said studies had shown no link between prescribed use of those drugs and later abuse.

Dr. Jeff Jonas, Shire’s senior vice president for research and development, said that the company was greatly concerned about the misuse of its stimulants but that the rate was very small. “I’m not aware of any systematic data that suggests there’s a widespread problem,” he said. “You can always find people who testify that it happens.”

Students who sell prescription stimulants to their classmates focus on their burdens and insecurities. One girl who sells to fellow students at Long Beach High School on Long Island said: “These kids would get in trouble if they don’t do well in school. When people take tests, it’s immediately, ‘Who am I getting Adderall from?’ They’re always looking for it.”

Every school identified in this article was contacted regarding statements by its students and stimulant abuse in general. Those that responded generally said that they were concerned about some teenagers turning to these drugs, but that their numbers were far smaller than the students said.

David Weiss, superintendent of Long Beach Public Schools, said the survey his district used to gauge student drug use asked about only prescription medications in general, not stimulants specifically.

“It has not been a surface issue for us — we’re much more conscious of alcohol or other drug use,” Mr. Weiss said in a telephone interview. “We haven’t had word that it’s a widespread issue.”

Douglas Young, a spokesman for the Lower Merion School District outside Philadelphia, said prescription stimulant abuse was covered in various student-wellness initiatives as well as in the 10th-grade health curriculum. Mr. Young expressed frustration that many parents seemed oblivious to the problem.

“It’s time for a serious wake-up call,” Mr. Young said. “Straight A’s and high SAT scores look great on paper, but they aren’t reflective measures of a student’s health and well-being. We need to better understand the pressures and temptations, and ultimately we need to embrace new definitions of student success. For many families and communities, that’s simply not happening.”

Fooling the Doctors

During an interview in March, the dealer at Lower Merion High reached into his pocket and pulled out the container for his daily stash of the prescription stimulants Concerta and Focalin: a hollowed-out bullet. Unlike his other products — marijuana and heroin, which come from higher-level dealers — his amphetamines came from a more trusted, and trusting, source, he said.

“I lie to my psychiatrist — I expressed feelings I didn’t really have, knowing the consequences of it,” he said, standing in a park a few miles from the high school. “I tell the doctor, ‘I find myself very distracted, and I feel this really deep pain inside, like I’m anxious all the time,’ or something like that.”

He coughed out a chuckle and added proudly, “Generally, if you keep playing the angsty-teen role, you’ll get something good.”

Christine, a junior sitting nearby, said she followed the well-known lines to get her drugs directly and legally, a script for scripts. “I’m not able to focus on schoolwork,” she said in a mockingly anxious voice. “I’m constantly looking out the window.” Although she often uses the drugs herself, snorting them for a faster and more intense effect, she said she preferred to save them for when her customers crave them most.

“Right before everybody took the PSATs, a bunch of kids went to the bathroom to snort their Addies,” she said.

This is one of the more vexing problems with stimulants in high schools, experts said — the drugs enter the schools via students who get them legally, if not legitimately.

Older A.D.H.D. drugs required low doses every few hours, and schools, not wanting students to carry the drugs themselves, had the school nurse hold and dispense the pills. Newer long-lasting versions like Adderall XR and Vyvanse allow parents to give children a single dose in the morning, often unaware that the pills can go down a pants pocket as easily as the throat. Some students said they took their pills only during the week and gave their weekend pills to friends.

The mother of one high school freshman in Westchester County said she would open the kitchen cabinet every morning and watch her son take his prescribed dose of Ritalin. She noticed one day that the capsule was strangely airy and held it up to the light. It was empty.

“There were a few times we were short in the month, and I couldn’t understand why,” recalled the woman, whose son was in eighth grade at the time. “It never dawned on me until I found those empty capsules, and then I started discovering the little packets of powder. He was selling it to other kids.”

A number of teenagers interviewed laughed at the ease with which they got some doctors to write prescriptions for A.D.H.D. The disorder’s definition requires inattentiveness, hyperactivity or impulse control to present “clinically significant impairment” in at least two settings (school and home, for example), according to the Centers for Disease Control and Prevention. Crucially, some of this impairment must have been in evidence by age 7; a proper diagnosis for a teenager claiming to have A.D.H.D., several doctors said, requires interviewing parents, teachers and others to confirm that the problems existed long before.

Many youngsters with prescriptions said their doctors merely listened to their stories and took out their prescription pads. Dr. Hilda R. Roque, a primary-care physician in West New York, N.J., said she never prescribed A.D.H.D. medicine but knew many doctors who did. She said many parents could push as hard for prescriptions as their children did, telling her: “My child is not doing well in school. I understand there are meds he can take to make him smarter.”

“To get a prescription for Adderall was the Golden Ticket — it really was,” said William, the recent graduate of Birch Wathen in Manhattan.

A high school senior in Connecticut who has used his friend’s Adderall for school said: “These are academic steroids. But usually, parents don’t get the steroids for you.”

As with the steroids taken by athletes, the downside of prescription stimulants appears after they provide the desired short-term competitive benefits. This was the case with a recent graduate of McLean High School in Virginia, one of the top public schools in the Washington area.

Late in his sophomore year, the boy wanted some help to raise his B average — far from what top colleges expected, especially from a McLean student. So he told his psychologist what she needed to hear for a diagnosis of A.D.H.D. — even gazing out the window during the appointment for effect — and was soon getting 30 pills of Adderall every month, 10 milligrams each. They worked. He focused late into the night studying, concentrated better during exams and got an A-minus average for his junior year.

“I wanted to do everything I could to get into the quote-unquote right school,” he recalled recently.

As senior year began, when another round of SATs and one last set of good grades could put him over the top, the boy said he still had trouble concentrating. The doctor prescribed 30 milligrams a day. When college applications hit, he bought extra pills for $5 apiece from a girl in French class who had fooled her psychiatrist, too, and began taking several on some days.

The boy said that as his A-minus average continued through senior year, no one suspected that “a kid who went to Bible camp” and had so improved his grades could be abusing drugs. By the time he was accepted and had enrolled at a good but not great college, he was up to 300 milligrams a day — constantly taking more to stave off the inevitable crash.

One night, after he had taken about 400 milligrams, his heart started beating wildly. He began hallucinating and then convulsing. He was rushed to the emergency room and wound up spending seven months at a drug rehabilitation center.

To his surprise, two of 20 fellow patients there had also landed in rehab solely from abusing stimulants in high school.

“No one seems to think that it’s a real thing — adults on the outside looking in,” the boy said. “The other kids in rehab thought we weren’t addicts because Adderall wasn’t a real drug. It’s so underestimated.”

‘No Way You’d Notice’

The Sklar family lives near the top of a daunting hill in Ardsley, a comfortable suburb north of New York City. Ardsley High School sends dozens of graduates every year to Ivy League-caliber colleges. When students there use Facebook, they all know that its founder, Mark Zuckerberg, once walked the same halls.

At their kitchen table after school last month, Dodi Sklar listened as her ninth-grade son, Jonathan, described how some classmates already abused stimulants — long before SATs and college applications. An accomplished student who said he would never join them, Jonathan described the ease with which he could.

“There’s no way you’d notice — that’s why so many kids are doing it,” he told his mother. “I could say I’m going for a run, call someone I know who does it, get some pills from them, take them, come home and work. Just do it. You’d be just glad that I was studying hard.”

His mother sighed. “As a parent you worry about driving, you worry about drinking, you worry about all kinds of health and mental issues, social issues,” she said. “Now I have to worry about this, too? Really? This shouldn’t be what they need to do to get where they want to.”

Asked if the improper use of stimulants was cheating, students were split. Some considered that the extra studying hours and the heightened focus during exams amounted to an unfair advantage. Many countered that the drugs “don’t give you the answers” and defended their use as a personal choice for test preparation, akin to tutoring.

One consensus was clear: users were becoming more common, they said, and some students who would rather not take the drugs would be compelled to join them because of the competition over class rank and colleges’ interest.

A current law student in Manhattan, who said he dealt Adderall regularly while at his high school in Sarasota, Fla., said that insecurity was a main part of his sales pitch: that those students “would feel at a huge disadvantage,” he said.

William, the recent Birch Wathen graduate, said prescription stimulants became a point of contention when a girl with otherwise middling grades suddenly improved her SAT score.

“There was an uproar among kids — some people were really proud of her, and some kids were really jealous and mad,” he recalled. “I don’t remember if she had a prescription, but she definitely took more than was prescribed. People would say, ‘You’re so smart,’ and she’d say, ‘It wasn’t all me.’ ”

One sophomore at Harvard-Westlake School in Studio City, Calif., is unsure what his future holds. Enrolled at one of the top high schools on the West Coast, he said he tried a friend’s Adderall this semester but disliked the sensation of his heart beating rapidly for hours. He vowed never to do it again.

But as he watches upperclassmen regularly abuse stimulants as they compete for top college slots, he is not quite sure.

“Junior and senior year is a whole new ballgame,” the boy said. “I promised myself I wouldn’t take it, but that can easily, easily change. I can be convinced.”