Penncrest High School's senior prom last month was a success, by all accounts.

But it was only one year ago that principal Rick Gregg dropped some ugly truths on a group of unsuspecting parents.

The students at school-sponsored dances, he told them, weren't exactly doing the fox trot.

"There would be a tight cluster of students . . . and in the center we had no idea what was going on," said Susan Nolen, copresident of the Parent Teacher Group and mother of two students at Penncrest. "Clearly, there was inappropriate touching; that was obvious during the cleanup of the dances."

Whoa - wait. What?

"The custodial staff were," Nolen explained, uneasily, "cleaning bodily fluids off the floor."

The parents were speechless, too.

So, after two years of unsuccessfully battling the problem, Gregg proposed at that spring meeting a solution now being tried by high schools across the country and by a growing number of schools across this region: a dance contract.

Penncrest's version, one of the first in the area, was mailed to students in the summer to be signed on the first day of this school year. (It was also adapted in December for use at Radnor High School.) It requires students to take a breath-alcohol test and undergo a bag search, but it also aims squarely at preventing "sexually suggestive dancing."

To attend dances, the contract states, students must agree to avoid "grinding, freaking or any mimicking of sexual acts"; "front-to-back touching"; straddling one another; or doing anything that requires resting their hands on their knees or the floor.

In short, they're not to do anything seen on MTV.

As solutions go, the contracts, once implemented, have proven relatively effective. Because students dutifully followed the contract at Radnor this year, the requirements have been lifted for Saturday's prom. (Teenagers are less inclined to grind when they're wearing gowns, but that promised reward was also part of what principal Mark Schellenger believes made Radnor's contract so effective.)

And at Penncrest's senior prom, the kids danced appropriately, said Gregg.

Yet the path to dance contracts, locally and nationally, has been attended by protests.

Boycotts have taken place. Off-site dances have been staged. (In Salina, Kan., students went so far as to organize an alternative homecoming dance.) And, of course, Facebook groups were formed.

"'Freaking.' Ummmm, no one knows [what] that is," Radnor High freshman Sisi Gospodinov, 15, wrote on the wall of a Facebook group titled "School Dance Contracts are BS."

Still, several students have since admitted their favored dance form did sometimes go beyond the pale, specifically in the "huddle," or the "amoeba," as they call it.

"It used to be pretty inappropriate; I'm not going to lie," Radnor senior Spencer Holm said. He likened the dancing to strippers' moves. "The freshman girls used to be expected to dance a certain way, especially if they were there with an upperclassman, even if they didn't know him that well."

Local principals have been brainstorming for a couple of years on how to deal with the problem, either by warning the kids to change or enlisting student leaders to direct the cause. Many times, an administration would think the message had taken hold at one dance; then, at the next, things would be even worse.

And now on the Main Line and in the western suburbs, "at least half the schools have contracts" or are considering them, Schellenger says. He mentioned Upper Darby, Strath Haven, and Conestoga as schools that had discussed the possibility of contracts, though administrators there did not return calls for comment.

Still, not all schools have been convinced that a contract is necessary.

Marple Newtown High School principal Ray McFall says he's been weighing a contract, although simply warning students who cross the line has proven sufficient so far. "It just hasn't reached the tipping point yet," he said. "The contract would be a way to get ahead of the game, before it really gets out of control."

Jeffrey Nesbitt, principal at Haverford High School, indicated that behavioral expectations were nonnegotiable, at dances and elsewhere. "We have always expected students to follow school rules while attending dances," he said. "At this time, we do not have an additional contract" beyond those expectations.

At Lower Merion School District, which encompasses Harriton and Lower Merion high schools, there's no contract - because, except for the prom, there are hardly any dances. Ten years ago, the district instituted a specific policy banning "inappropriate" behavior at school-sponsored dances; about that same time students stopped organizing them, district spokesman Doug Young said.

The contracts at Penncrest and Radnor nearly brought about a similar end.

At Radnor, where Holm is on student government, he and the class president had to launch an epic e-mail and text-messaging campaign for the December senior semiformal trying to persuade classmates to give the contract a chance.

Boycotts were a bigger problem at Penncrest, where there was talk of holding an alternative no-contract prom. Two dances, one in November and one in December, were canceled due to lack of interest, said senior class vice president Colleen McGeehan, 18. She said last fall's homecoming dance sold 200 tickets, compared with about 600 the previous year.

At this year's Penncrest sophomore sock hop, there was even a case of not-so-civil disobedience.

"People were trying to get the dance shut down as a sign of resistance," said junior C.J. Cassey, 18. After two warnings by the administration - which blasted Frank Sinatra hits in an effort to subdue the mood - the students succeeded. "There were people who cheered and high-fived after the dance was shut down, which I feel is a shame."

As a student leader, McGeehan was expected to help sell the contract. The problem was, she wasn't sure she bought into it.

"A lot of kids felt like they were being directly attacked by the administration, like it was an attack on our culture. A lot of people were really offended, and I understood that," she said.

Still, Penncrest students said that by April's junior prom, they had reached a middle ground with the administration. Only six students were asked to leave that dance, which was considered a success.

The students also discovered a de facto loophole:

"Instead of grinding back to front, people could grind front to front," Cassey says wryly. "That was found to be less inappropriate by the administration, though that's been debated by the student body."

The administration does not actually condone front-to-front grinding. But how, after all, is it determined which teenage dance moves are OK? Gregg proposes the same litmus test Supreme Court Justice Potter Stewart once applied to pornography: I know it when I see it.

He freely acknowledges that there has always been, and probably always will be, a generation gap when it comes to dancing. But he also says today's "vertical lap dancing" is downright unsafe.

Gregg, a 29-year educator, remembers first seeing front-to-back dancing in schools in 1987, when DJs were playing George Michael's "I Want Your Sex." That is, perhaps not coincidentally, the same year Dirty Dancing was released.

But unlike wide-eyed Jennifer Grey, who wandered into the staff-only dance party at Kellerman's, local teens say grinding is just normal.

In some cases, it helps camouflage that some students can't actually dance.

Sarah Antonelli, a Penncrest senior, described grinding more as a comfort zone, an equalizer for the rhythmically challenged. Grinding barred, "you really don't know what else to do instead," Gospodinov said.

Even Holm of Radnor was skeptical until his first dance with the contract in place, held in December. "At first, people were timid," he said, "but over the first hour, they got on the dance floor and were dancing as if they were at a bar mitzvah or a wedding."

Now, "the whole atmosphere is different. It's so much better, in the sense that there's no pressure to dance" a certain way.

That's the point of the contract, says Gregg. It slows down kids who "are trying to be grown-ups before they're ready."