By the end of ``The Notebook Girls,’’ the story of four teens at an elite New York high school, the main characters have had the kinds of experiences that make parents cringe -- oral sex, the loss of virginity, binge drinking, pot smoking. But Julia, Sophie, Courtney and Lindsey have also matured. They’ve mended fences with their parents and thought deeply about the world. They’re on their way to college.

``Looking back on everything, I realized we all figured ourselves out in this mess,’’ Courtney writes in a farewell note to her pals. ``There’s nothing we can’t share.’’

The book is raw but also sentimental, the characters obsessed with making their way through high school’s cruel pecking order. Parents are the objects of complaint, but they’re on the periphery of the story. There’s despair, and a happy ending. It reads, in other words, like the typical ``young adult,’’ or YA, novel, found in the teen sections of bookstores and mostly written by adults. But ``The Notebook Girls,’’ which was published this month by Warner Books with a first printing of 40,000, is not a novel, it’s a real-life account written by four actual teenagers.

``We wanted to tell our story in our own words,’’ said Julia Baskin, one of the authors. After all, she pointed out, ``We lived through it.’’

Or, to put it more bluntly: Why let a bunch of middle-age people tell you what it’s like to be an American teen?

That attitude is spreading as more teenage writers storm the barricades of publishing, starting with the YA category but by no means ending there. Indeed, some titles that previously would have been seen as young adult are now also being marketed to adult readers.

``Why should I have to wait years to get a book deal?’’ said Robyn Schneider, a Barnard College student from Irvine, Calif., who is the author of the novel ``Better Than Yesterday,’’ which will be published by Delacorte in 2007 and is aimed at both audiences. She describes the book, written when she was 18, as the tale of ``four top students at an elite East Coast boarding school (who) run away to Manhattan, fall in love and learn to take the SATs a little bit less seriously.’’

While revenue in other sectors of the book industry remains flat, YA is booming. Sales for fiction alone have grown more than 23 percent in the last six years, and projections are for continued growth, even if you subtract the ``Harry Potter’’ books, according to Albert Greco, a Fordham University business professor who studies publishing trends. Girls make the vast majority of these purchases, and publishers have focused most of their marketing strategies on them, through hugely popular paperback series such as ``The Gossip Girls,’’ ``The Clique’’ and ``Making Out.’’

A key reason for the success of YA books, which run the gamut from romances to mysteries, thrillers to self-help, religion to sports, is that there are far more teenagers than there were 15 years ago. They’re part of the 12- to 21-year-old demographic that spends a staggering $170 billion annually on entertainment, including books.

Notwithstanding the case of JT Leroy, the adult who conned readers into thinking a cross-dressing teenage prostitute had written the well-received books ``Sarah’’ and ``The Heart Is Deceitful Above All Things,’’ publishers are increasingly willing to take teenagers seriously as the authors of adult titles.

This month, the adult division of Little Brown published ``How Opal Mehta Got Kissed, Got Wild, and Got a Life,’’ for which Harvard University sophomore Kaavya Viswanathan received a $500,000 advance as part of a two-book deal. She wrote the novel when she was 17. Her book, with comic echoes of ``Mean Girls’’ and ``Bend It Like Beckham,’’ tells the story of a brainy Indian American girl who is convinced she can’t get into Harvard unless she develops a personality and has a good time in high school. DreamWorks just bought film rights; the movie is being co-produced by Contrafilm and Alloy Entertainment -- which recently guided ``The Sisterhood of the Traveling Pants’’ to the screen.

``I don’t see a huge talent difference between one age group or another,’’ said Viswanathan, who finished her novel while she was taking five courses at Harvard and studying for finals. ``It all comes down to who has the dedication to sit down every day and put something on paper. It all starts from there.’’

These teen authors are not the first to find their way to publication, of course. Mary Shelley famously wrote ``Frankenstein’’ in 1816 when she was 19; Maureen Daly began writing ``Seventeenth Summer,’’ a 1942 title that many consider the forerunner of the modern YA novel, when she was 17; S.E. Hinton wrote ``The Outsiders,’’ a 1967 novel that became a cult classic and later a movie, at 16.

Some teen writers have made genuine splashes in recent years. Christopher Paolini began work on the fantasy novel ``Eragon’’ -- which has sold more than 1.5 million copies -- when he was 15. Amelia Atwater-Rhodes is the author of a series of popular fantasy novels, beginning with ``In the Forests of the Night,’’ which she wrote when she was 14. Nick McDonell produced ``Twelve,’’ a well-reviewed first novel, when he was 17.

This generation of teenagers seems less fazed by the challenges of writing a book and getting it published. They are, said Jen Bergstrom, publisher of Simon Pulse, a youth imprint of Simon & Schuster, ``surprisingly more literate than older generations would believe. It’s inevitable that they will find a way to get good manuscripts published.’’

Teenagers, after all, are forever sending text and instant messages. They spend hours updating blogs and keeping online journals. The discipline that adult wannabes fight so hard to master in night classes and writing colonies -- the need to write, write and write some more -- comes effortlessly to many teens. For them, daily life on the Internet has become an almost natural prelude to the writing of short stories, essays and novels.

``Text never went away for this generation; it’s very much a part of what we deal with every day,’’ said Ned Vizzini, who published his first book, ``Teen Angst? Naaah...’’ (Random House) when he was 18. ``I’m shocked by how many e-mails I get, maybe two or three a day, from people who say they’re teenagers and want to write a book. ... They think it’s a very cool thing to do, something with real permanence.’’

Today, the so-called echo boomers -- sons and daughters of the baby boomer generation -- ``are constantly putting their most personal thoughts out there on the Internet for others to see, and it’s a whole new world of emotions and ideas,’’ said Shirley Halperin, West Coast editor of Teen People magazine. ``If I was a publisher looking for young talent, I’d look through blogs and online publications.’’

Skeptics, however, say it’s one thing to blog, another to write a novel.

``I know that kids today are savvy and they have access to the means of getting published in a way they didn’t before,’’ said Elise Howard, editorial director of HarperTempest, a youth imprint. ``But I just don’t know if it will reach a critical mass.’’

``The Notebook Girls’’ owe the impetus for their book deal to Sophie’s parents, Randy Cohen, who writes ``The Ethicist’’ column for The New York Times Magazine, and Katha Pollitt, a Nation columnist and author. They saw some entries and suggested the material might become a book; a family friend put the girls in touch with agent David McCormick.

As they gathered recently at a coffee shop on Manhattan’s Upper West Side, the four girls -- now attending various colleges -- laughed over the humble origins of their writing project. The notion that they would be publicizing a spring release for Warner Books and appearing on the ``Today’’ show, seems as outlandish now as it did five years ago. Back in September 2001, Lindsey Newman, Sophie Pollitt-Cohen, Courtney Toombs and Julia Baskin were all freshmen at Stuyvesant High School, a public school for academically elite students, in lower Manhattan. The girls, who knew one another from middle school, were plunged into high school life in a particularly intense way: Their school, four blocks from ground zero, was briefly shut down after the 9/11 attacks, and pupils were relocated to a Brooklyn site.

The girls yearned for a way to stay in touch, to hold onto their friendships, in such a strange new world. So they hit on the idea of passing a notebook around to each other during classes, in which they could share thoughts on anything and everything. They wrote of boys and basketball, drugs and dating, politics and promiscuity. The bulging, handwritten notebooks, five in all, mingled personal and political anxieties: Lindsey, who is black, fretted over excelling in school and expressed her anger about discrimination. Julia agonized over her attraction to another girl and passionately defended Judaism against critics. Sophie obsessed over boys and said Americans should mourn all victims of terrorism, not just those who died at ground zero. Courtney eventually swore off pot and vowed never to forget 9/11.

They felt that few adults understood them. As others at the table nodded, Courtney said, ``Your parents think you just get on the school bus in the morning and you sit in your class all day, and you go somewhere and you come back. They don’t realize that you live this entire life that they really don’t know about.’’

The publisher condensed the five notebooks into one, but preserved the girls’ original handwriting. Although names of fellow students and other characters were changed to protect their privacy, the content was left untouched -- including sarcastic comments in the margins, racy, anatomically correct cartoons and black-and-white photographs of the four authors, some fetching, some unflattering.

Caryn Karmatz-Rudy, who edited the book, said she has suggested to the four authors that they preserve their voluminous daily e-mail correspondence. Might there be a second installment, ``The Notebook Girls in College,’’ she wondered?

``Whoa,’’ Lindsey said. ``A career in writing -- and I hope I’m speaking for all of us -- is not something we’re all interested in. But writing is a big part of who we all are.’’