On a lit theater stage in Long Beach, Vince O'Connell cuts a dashing figure. He stands with his back to the audience in clothes that evoke Midtown Manhattan in the late Eisenhower period: slim-cut black suit, white shirt, narrow red tie. He is 18 years old.

Downstage is 17-year-old Erica Williams. In a blond updo and midnight green cocktail dress, Erica has the look and bearing of a Hitchcock film siren.

Out of sight, an instrumental combo plays a dramatic, minor-key overture, and Williams begins twirling vampishly around O'Connell. He turns, flips on a Fedora and sings the opening lyrics to “Cry Me a River.”

Forty-two other teen performers — half boys, half girls, all in similar period attire, all students at Los Alamitos High School — join in the song-and-dance number. If you've ever wondered what Mad Men would look like as a Broadway musical, here's your answer.

This is show choir, a performance-art genre that exists almost exclusively at the high school level. Student ensembles perform mash-ups of pop hits and showtunes set to group-dance routines.

Swing, hip-hop, jazz and ballroom are key ingredients in the choreography. As an aesthetic experience, it's a hybrid, with its DNA spliced together from opera, cabaret, vaudeville and the modern music video. If done poorly, it's accidental camp. If done well, it's a fizzy, thrilling delight.

Long an ignored backwater of high school music departments, show choir is in the early stages of cultural ascendancy in L.A.

Serving as launch vehicle is Glee, the Fox TV series about a show-choir troupe in a fictional Ohio high school, is a critical favorite and modest ratings hit and has had a legitimizing influence. Joel Biggs, the president of FAME Events, a national promoter of show-choir competitions, credits Glee with growing public interest in his company's productions. The Los Alamitos kids say that Glee has enhanced show choir's standing in the school's social ecosystem.

On March 6, FAME held its annual West Coast competition at the Terrace Theater in Long Beach. On that morning, the lobby was a hive of adolescents prepping makeup and costumes. A kiosk sold T-shirts reading “Caution: Jazz Hands” and “Show Choir Rocks.” Backstage in the green room, the Los Alamitos mixed choir, which goes by the name Sound FX, was put through final paces by David Moellenkamp, its faculty director.

Moellenkamp is a tall, angular Paul Rudd look-alike, with a brisk but friendly manner. In his 18th year of coaching show choir, he is exacting and accomplished. He directed the 2008 show-choir national champions.

“You have a tradition to uphold,” he told them this day. “And you have something to show off.” That was the pep talk. It wasn't any longer because it didn't have to be. Moellenkamp knew that his kids were ready, and they knew that they were ready. Preternaturally composed, the members of Sound FX looked like they hadn't known stage fright since they were 5 years old.

It was clear early on that Sound FX was the horse to beat. The only other plausible contender was the mixed choir from Newhall Hart, Sound Vibrations. (All show choirs have names like these, usually involving Music or Sound as root words.) Sound Vibrations' set borrows puppet-theater imagery to play on themes of young-adult autonomy in a visually aggressive style. It's entry-level Lady Gaga stuff, and somehow it works.

Three judges grade each performance on choreography, show and vocals. At a rehearsal a few weeks before the event, Moellenkamp told his kids, “Seventy percent of you are doing it, but your scores come from the lowest 30 percent.”

None, however, will admit that winning is paramount or even interesting. “It's nice, but the process is what's important,” Williams told me.

The response seemed unnaturally adult, a talking point that was too on the nose. In a side hallway after the sets but before the winners were announced, I pressed Moellenkamp on it. Weren't his kids anxious to hear if they'd won? “No, I don't think so,” he said. “I try to teach them not to put their self-worth in the hands of the three judges.”

The scene back inside the auditorium vindicated him. As they awaited the judges' scores, members of the competing choirs circulated. Laughter, bubbly teenage patter — there was an untroubled energy.

To kill time, a FAME staff member cued up music on the theater's sound system. It was “Crazy” by Gnarls Barkley, and it ignited the room. Kids from all schools rose from their seats and began bopping to the song. They all knew the words. They were all great dancers. They seized the moment to cross over to their competitors' sections to groove with kids they probably had not met.

They were reveling in their youth and talent, and there was no question they'd have preferred to keep doing this than hear what the judges had to say.

The adults in the crowd, parents mostly, traded looks of pride and amusement. Whatever we were up to at that age, the glances seemed to say, none of us was having this much fun. If only we'd done show choir.

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