In 1979, Rolling Stone wunderkind writer Cameron Crowe, who had graduated from high school in 1972, went back. For a year, "from first bell to last bell," he was Dave Cameron, quiet, unassuming senior at a Redondo Beach, Calif., high school. Crowe lived to write about it -- more from the social than the academic side, and totally from his contemporaries' point of view -- in "Fast Times at Ridgemont High." As night follows day, a film has followed the book; it opens today.Crowe proved you can go back to home room again.

"Fast Times," fast, simplistic and directed at the kids who inspired it, rang with a certain truth and poignant humor in its everykid dialogue and its catalogue of adolescent obsessions and activities -- fast food joints as the sole sources of nourishment and employment; courtship rituals between confused girls who learned about sex before romance and awkward boys who blundered through both; casual drugs, false maturity, social competition, the desperate prepping for life or college (whichever encroached first).

Within its flowing anecdotal vignettes, six young characters eventually found their author, though their names had to be changed, presumably to protect what little innocence there was. Margaret Mead or Robert Coles might have probed more deeply, but it's doubtful they would have gotten so close to the heart of adolescence.

It helped, of course, that the then 22-year-old Crowe didn't look a day over 17, that his hair hung well below his shoulders, that the "standard Southern California attire" -- tennis shoes, T-shirt and backpack -- clung naturally to his lanky frame, that his laconic manner was genuine. He slipped undercover so smoothly that none of the Ridgemont kids ever suspected he was anything more than a transfer student.

Crowe spent nine months at Ridgemont, and "it was like the senior year I never had," he recalls. "Actually, until I started to fit in with the students and make friends with them, there was a different book on its way to being written, about me going back to recapture a little bit of my adolescence." The bright son of a teaching mother, he'd skipped three grades and graduated at 15, "so I'd never really had that high school experience."

At about the same time, the precocious Crowe had started writing for pop music magazines, notably Circus, Creem and Rolling Stone. "I'd come home from doing stories and my parents would say, 'That's very nice, but don't you think you should spend some more time cruising around, being a kid, partying and everything?' It didn't occur to me until later that this was one of the fascinations of going back."

"Going back" had been suggested by agent David Obst, who felt that after seven years of personality profiles for Rolling Stone, Crowe was ready to move between harder covers.

When the idea of posing as a student came up, Crowe sensed a great opportunity. He approached the principal at Ridgemont, a Redondo Beach public school not far from where he'd grown up, and arranged for his "inconspicuous presence" for a year. The only other people who would know his real identity were a homeroom teacher and five instructors. Crowe took on a light schedule, which may be why there's not a lot of academic activity in the book or the film; classrooms were the commas in long sentences of socializing.

Once in, Crowe grappled for a few weeks with "am I being a spy? Is this the right way to go about this?" For the first month, he was virtually ignored. "But once I started getting into groups, the more I hung out with the kids, the book started changing. I believed I could do teen-agers a service because so much about them is written at arm's length. The kids that get the publicity most of the time are like Brenda Spencer, who shot six people because she was bored, or the angel dust cases or Why Johnny Can't Read. I thought these kids were a lot smarter than they were being given credit for. They're anonymous Joes who are not unwed mothers or angel dust cases; they're just average kids slugging through life. When I saw the inner trauma in these kids' lives, I started getting excited."

Crowe went in as a camera, kept copious notes, often running off to the bathroom to get things down before he forgot them; he says he earned a reputation as "the guy with the bad bladder." He used a tape recorder early on, walking around the campus and catching casual conversations, but put it away after a suspicious Ridgemont cheerleader challenged him while he was taping a practice session: "Are you from crosstown arch-rival Lincoln? We really don't like our cheers to get out." Crowe brought it out of mothballs only at year's end, to tape a series of "What I'm Going to Do With My Future" speeches.

He lived at home with his parents, hiding correctly addressed magazines when his new friends would come over. As a student he was quiet, reserved. "The first time around I'd been a class clown, a prankster," Crowe laughs, "which was the natural thing to cover up for being young. I couldn't tan and that was a major problem, because it was a beach community. This time, I turned into the student I really disliked . . . but I also got a tan for the first time in my life -- that surprised my mom more than anything. And I really got into surfing and partying." His first real connection with the students was made "when a bunch of us went to see a Chuck Norris film at the drive-in."

As the book came together, Crowe made a hard decision -- to keep himself totally out of the book. Crowe focused on six major characters, the most important being Linda Barrett, the sophisticated 17-year-old who had somehow convinced everyone she'd seen and done it all; she became Crowe's Baedeker, opening the doors of reserve so natural to adolescents. The other continuing characters were the preppish brother and sister, Brad and Stacy Hamilton, whose lives revolved around their fast food jobs and shared sexual awkwardness; Jeff Spiccoli, the good-as-Acapulco-gold surfer who wandered through Ridgemont in a happy daze; Mike Damone, the transplanted Philly greaser and master of The Attitude; and the wimpy Mark "Rat" Ratner. They were, Crowe admits, stereotypes, but "I wanted types that people knew . . . and high school is populated mostly by stereotypes."

A week after graduation, Crowe started coming out, calling the Ridgemont kids and re-interviewing them, corroborating his notes and the stories he'd heard. Most were surprised at the deception, but none was bothered. He'd blown his cover only three times, purposely, to Stacy and Linda and to Mike Damone, who made his money scalping rock concert tickets. "He asked me what Led Zeppelin and Jimmy Page were like, so I started into a long rap, but he just said, 'Cool, let's go to the beach.' He really didn't want to hear that much about it."

The actual writing of the book was not the most warming experience, Crowe says. The intense boredom of high school, central to his experience, was excised in favor of racier anecdotes; identifying characteristics had to be submerged as a legal precaution; at one point, after the success of "The Preppy Handbook," serious thought was given to "cutting it in half, putting in lots of pictures and a glossary of high school terms."

Most of the references to rock 'n' roll were also cut out, Crowe complains, even though "music was running through all their lives at all times."

Sex and, to a much lesser degree, drugs, became the ruling motifs. Crowe himself dated "lightly" at Ridgemont ("my agent had said there was a 'morals clause' in the contract and I believed him!"), but became a confidant to the two girls who inspired Linda and Stacy, especially after they knew what he was up to. "They told me outrageous stuff, offered to have girls over for an overnight party and tape it. I told the kids I wouldn't write about things if they felt it was an invasion of privacy. In the end, no one said, 'You can't write about any of this.' In fact, they wanted their real names used but part of the deal with the school was to change the names. In the end, though, the story belonged to the kids."