Backstage at Prabal Gurung's spring 2012 show Saturday.[Photo/The New York Times]

Fourteenth Street was mildly crowded as the couple walked west in the approaching twilight of last Friday. Something about the way they looked suggested that they were headed to Milk Studios, the fashion show site on West 15th Street, and that it might be interesting to follow them.

The woman, her bleached-blonde hair spilling past her small shoulders, had on a sleeveless dress of thin white crepe that the breeze occasionally caught and blew around her thighs. Underneath she wore black full-cut underpants that were visible through the crepe, an obviously considered choice since her bra more conventionally matched her dress. She had on platform sandals.

Just before the light at Ninth Avenue, two guys, walking in the opposite direction, turned their heads and let out a long "Zzzssh." It would be difficult in that neighborhood, during Fashion Week, with models everywhere, to be surprised by a person's outfit, but the young men seemed genuinely so. The couple entered 15th Street.

She gave her name as Lara Jade — or, rather, the man with her did, preceded by, "She's a very famous photographer." This was pure bluster but hardly the point. She was striking looking, with kittenish features, and her Web site gave her age as 22. The man, who called himself James Zanoni and said he was a motion graphics designer in New York ("for now"), looked to be about the same age. As the sidewalk in front of Milk filled up with guests and street photographers, Mr. Zanoni and Ms. Jade were asked why they thought so many young people wanted to attend the shows, in contrast to those whose jobs largely require them to be there.

"To stand out," Mr. Zanoni replied quickly.

"Definitely," Ms. Jade said. "To be seen and to see what's new."

At no time during Fashion Week is this astonishingly ordinary wish more obvious and so easily met than on Friday and Saturday, when the schedule is crowded with young designers — Alexander Wang, Joseph Altuzarra, Rag & Bone — and parties, like Mr. Wang's at Pier 40 late Saturday night, which had the quality of a rave.

For those partygoers, in their skimpy dresses and bra-revealing tank tops, who were not repelled by the initial invectives of the hip-hop group Odd Future, who stayed and danced, the party gave glimpse to a reality quite apart from the scene at Lincoln Center, with its commercial air and overly dressed guests, and even from the fashionable scene at Mr. Wang's show. "That's when things got really cool," a 30-something guest said.

In a matter of a few seasons, the Friday and Saturday shows have eclipsed the others in excitement and energy, so much so that, by Sunday, it seemed to many that spring 2012 Fashion Week had peaked and that the remaining days, far from being a slalom, were a slog. As it was, the scenesters had pretty much evaporated — no more black-underwear girls — and the plaza at Lincoln Center had depressingly filled up with claimers and gawkers, like a leaf-strewn swimming pool.

Beyond energy, though, what do all of these young people bring to the communal fashion table, and what, specifically, do they give to designers? And what, apart from the thrall of being at a show, do these designers give in return? At a time when style is organic and homegrown, and for reasons of both taste and cost, is more and more divorced from the system of editors and designers, is there an actual creative exchange that advances American fashion?

Perhaps unsurprisingly, the answers to these questions point to a divide between young fashionistas and front-row types that has been stretched far beyond generational lines — by blogs, fast fashion and other factors. Andrew Rosen's decision to hire the fallen Paris star Olivier Theyskens for Theory, which Mr. Rosen founded, seemed to recognize the gap; Mr. Theyskens's second show, on Tuesday, drew raves for its relaxed blazers and hip-hugging bottom-sagging jeans, which will cost a few hundred dollars. But such farsightedness is unusual.

"What's interesting to me about the Saturday shows," Mr. Altuzarra said, "is that they have the feeling of a split personality. They're a bit of an industry party with professionals attending." Last season, when Mr. Altuzarra showed at Milk Studios, the halls were jammed with people hanging out or dropping by other collections, like Suno and Billy Reid. It was a fun scene but also a problem for Suno, a relatively new label designed by Erin Beatty and Max Osterweis. The buyers from Saks couldn't get into the presentation. This season, the designers cut their guest list back sharply to make sure the pros could see what they had come for.