The Philadelphia Museum of Art experience is usually quiet and reverent. Patrons, if they talk at all, keep their voices to a hushed whisper. They linger for a couple dozen seconds or so in front of each piece of art as they make their sedate, silent circuit of each room as if on an invisible conveyor belt, hands clasped lightly behind their backs.

But there’s something about the portraits photographer Mary Ellen Mark captured of teens at their high school formals that seems to loosen the tongue. On a recent day at Mark’s show “Prom” in the Perelman Building, people weren’t afraid to rise above a whisper. They pointed, giggled and sighed wistfully, unafraid to voice thoughts like “I really hate that dress” or “Her eyebrows look good.” While many of these comments were fairly inane, there was an overall feeling of participation — people were having fun, looking at the photographs for a little bit longer than they usually would and bringing something of themselves to the experience.

All the fuss was over a collection of about 60 black-and-white, 20-by-24-inch photographs Mark shot with a Polaroid Land Camera (one of only five in existence, with precious little film stock remaining) between 2006 and 2009 at 13 high school proms in Pennsylvania, New Jersey, New York, California, Texas and Virginia. (One of the schools visited by Mark, a native Philadelphian and Penn grad, was her own alma mater — Cheltenham High School in Wyncote.)

Each print is unique — literally, there are no negatives — but the images, taken as a whole, have some common threads familiar to most people who attended an American high school. For one, the prom-picture ritual itself: Two dressed-to-the-nines teenagers pose together, centered against a neutral backdrop. ( “Prom” also includes intermittent singles or groups, such as an image of one thrilled-looking young man accompanied by two unsmiling blondes.)

Individual prom pictures are, obviously, not interesting enough to be hung in an art museum. But in the context of each other, these photographs are more than the sum of their parts. They’re a freeze-frame of the different ways that kids of various socio-economic backgrounds, races and sexual orientations all participate in this most American of experiences.

Not everyone is attractive in the photographs, exactly, yet they all are beautiful. Each subject is a blank slate for projected narratives and backstories. A fresh-faced young woman in a tiara tightly grips the arm of her tuxedo-clad, Bieber-haired girlfriend. Two overweight Texan sisters in puffy dresses keep a foot of space between them. A white dress must have been altered to accommodate a basketball-sized pregnancy. Some kids hang off each other, others leave ample room for Jesus. Some kids look streetwise and tough; others look as if they were regularly shoved into lockers.

Accompanying the photographs is a 33-minute video by Mark’s husband, filmmaker Martin Bell — a series of interviews with the subjects of the photographs that confirms some of these narratives and assumptions while undermining a few more. The prom queen is naive and somewhat full of herself. The beautiful cancer survivor is sweet and wise. The nerdy-looking couple is ... well, really nerdy. But the tough-looking Latino couple from New York who mean-mugged the camera are teary-eyed and sentimental. Some of these kids love each other, while others are realists, expecting to go their separate ways in the near future.

The level of trust Mark and Bell were able to earn from their subjects is remarkable. These subjects appear heartbreakingly young and innocent; it’s hard not to imagine how much they’ll change in a few short years, and to wonder if the picture will one day embarrass the hell out of them.

A few people (myself included) discreetly wiped their eyes more then once during the film, temporarily possessed by the spirit that makes moms across all cultures sniffle, “My baby’s all grown up.” Even if you hated high school, you can’t help but feel like the kids in America are doing all right — even if they seem a little misguided at times.

(annette.monnier@citypaper.net) (@onereviewamonth)

“Prom: Photographs by Mary Ellen Mark,” through Oct. 28, included in $20 admission, Philadelphia Museum of Art, Perelman Building, 2525 Pennsylvania Ave., 215-763-8100, philamuseum.org.