It's nearing midnight on graduation night, and 200 South Lakes High School seniors are crowded outside the Reston Community Center, waiting to join 100 classmates already inside. Dressed in jeans, tennis shoes, shorts and other casual wear, the seniors are vying for an unlikely opportunity: a chance to attend a nonalcoholic party sponsored by their parents.

On a night traditionally reserved for wilder bashes, 300 of the school's 570 seniors opted for the event.

"I'm surprised," was the refrain uttered by graduate after graduate, amazed that so many peers chose to attend.

"Everyone laughed at it," Amy Skubal, 17, said of the initial response to the party.

"Everyone kept saying, 'Are you gonna go? Are you gonna go?' and everyone said, 'Maybe,' " said Hilary English, 18.

She said people were hesitant, "like we were all too cool to say, 'I'm definitely going.' " But, by all accounts, the All Night Party proved a success.

By 12:30, the party was hopping. While some danced barefoot and free to the music of a band, the Magnets, others moved throughout the community center, scouting out food and games.

There was the Tahiti Room, where they could order virgin daiquiris and pina coladas; a cafeteria full of pizza, cheeses and meatballs; a cosmetic makeup room; and a room with a fortuneteller. Near the front of the center, which was decorated with posters and balloons, a television played a videotape of their graduation ceremony, held just a few hours earlier, a photographer took pictures and artist Marcia Klioze drew caricatures.

"We knew {the students} would have a good time when they got here," said popular physics teacher Vince Mosconi, who chaperoned the party. "But we had to get them here."

The idea of a parent-sponsored event, without alcohol, came from Betty Peterson, who moved to Reston two years ago from Corvallis, Ore. "In Corvallis, they've been doing this for over 30 years," said Peterson. So when her son Jeff was nearing graduation, Peterson, who assumed the parent-party tradition thrived in Northern Virginia, called South Lakes to volunteer her services. "They didn't know what I was talking about," Peterson said. But Peterson soon got in touch with school counselor Kay Fletcher, who placed Peterson in contact with mothers who might like such an idea.

By February, Peterson, party coordinator Caren Schumacher and a few other mothers were working 30 to 40 hours a week, planning the event that was to be a safe, fun, special gift to their children. The result was "totally different than what we had in Oregon," Peterson said, noting the exceptional response of the Reston business community. More than 150 businesses donated prizes, cash and everything from the money used by the gamblers to the airport-like check-in stand that greeted the graduates as they entered the community center.

Monte Carlo, the casino room, where all the mock-gambling took place, was the night's most popular scene, as seniors came by to play the likes of roulette, blackjack and dice for portable radios with headphones, large sombreros and other treats donated by businesses.

By sunrise Friday morning, about seven hours after the doors to the community center opened at 11 p.m. the night before, the verdict was in. "I'm tired," said English, who is going to Radford University to major in English. "But it was fun and I enjoyed it. Twenty years from now I'll look back on this and this will be a happy memory."

At 5 a.m., Schumacher began handing out prizes. The seniors still at the party crowded around the edges of the dance floor, some standing, others sitting on tables. First came $50 prizes, then six $250 prizes, four $500 prizes and a grand prize of $1,000.

Mitch Isaacs, 18, who will attend Virginia Tech to major in engineering, won $500. Isaacs, like most of those gathered, would be off the next day to Ocean City for a week of beach fun. "This was a real good idea . . . I'm thinking about staying back and doing this again," he said.

By 6:05 a.m., the center had emptied out except for a few students and the 20 adults taking down the party ornaments and cleaning up. Two fathers, Rich Huck and Ed Schumacher, were slumped back in chairs along the center's wall.

"Yeah, we're all out of gas," said Ed Schumacher, who filmed the party with a video camera. "We're running on fumes," said Huck, with a tired chuckle. The party had proceeded perfectly, the graduates had had a good time and the two men appeared as happy as they were exhausted. "I think we probably started a tradition," said Ed Schumacher.