The gathering started off with just two friends, but there was no chance it would stay that way. The tenth grader had already let it slip, telling another friend the vital piece of information that can spread like wildfire among teenagers.

She had said her parents were away, gone off-Island for the weekend.

"I said they could come over. Then 10 cars showed up. People were just kind of walking in," she said. "I guess they thought there was a party. I told them, ‘You guys can stay for an hour,' but people just ended up staying longer."

Then more came - juniors, seniors - faces she recognized from school, but not all ones she knew. By the time kids cleared out at around 1 a.m., the house had taken the brunt of partying teens. A kitchen cabinet had been pulled loose from the wall after a fight broke out. Holes were punched in two screen doors, a case of CDs was missing and there were broken glass and empty bottles around the yard.

"The more you say ‘get out of here,' the more some say ‘we're not leaving,'" said the girl. "All that was going through my head was I wish I hadn't invited kids over."

Sadly, what happened to this high school sophomore in the fall is not an isolated occurrence. Teens, police, school leaders and parents who have learned the hard way say it's really the norm - and fueled by the advent of new technology that makes communication between would-be partygoers instantaneous.

"Most kids have a cell phone," said Curtis Chandler, 16.

Driving around the Island on a weekend night with her friends, said 17-year-old Olivia Lew, "there's always a phone ringing."

The upshot is what West Tisbury police chief Beth Toomey calls the spontaneous party.

"They all have cell phones and say ‘No one's home at so-and-so's,'" said the chief. "They can do a large gathering quickly."

For many teenagers, such spontaneity is a fact of life. "When I leave my house and my parents ask me where I'm going, I say, ‘I'll call you when I find out,'" said Miss Lew. "What tends to happen, it ends up being a party train, up to 20 cars following each other from house to house."

And in the majority of cases, those houses have one thing in common - no parents at home. "Ninety-five per cent of the time, there are no adults around," Miss Lew added. "Teens are looking for some place where they can be themselves."

Young people like Miss Lew and Mr. Chandler admit things can get out of hand at such parties, but they say that most kids respect other people's property.

Chief Toomey is not convinced. In her view, teenagers, alcohol and no supervision are a volatile mix.

A spontaneous party "is one of the most dangerous types," she said. "In a large group, it's easier for someone in trouble with alcohol to get lost in the crowd, and no one notices."

After one party last fall in West Tisbury, a senior from the high school ended up in the hospital emergency room with alcohol poisoning. At another party, kids tromped into the woods looking for a boy who had wandered outdoors and was missing.

With drinking and drug use going on, said Chief Toomey, the inevitable consequence is bad choices being made. "The inhibitions leave," she said. "There's poor decision-making about drunk driving, and poor decisions about sex or drug-taking with alcohol."

While none of that news surprises high school guidance counselor John Fiorito, what does stand out for him in the high school party scene is the mixing of grades.

"There's four grades of kids fighting for the few parties. It's a new phenomenon," he said. "What I remember was that if it was a senior's house, it was a senior party. There was some sort of divider. Now, the younger kids are in over their heads because the older kids are around."

The fact is, by the time most high schoolers are upperclassmen, they know better than to tell anyone their parents are leaving town. That leaves the younger ones to learn a hard lesson.

"There's always those people who are waiting to hear those magic words - my parents are away," said Miss Lew.

While the younger students appear to be less savvy about the risks, some parents aren't much better.

"Everybody thinks it's such a safe place," said Mr. Fiorito, "but it's a false feeling of safety."

The mother of that tenth grader is no longer so naive. The plan to leave their teenage daughter with their older son didn't exactly work. The brother went out, and the sister was overrun.

"I was upset and angry and shocked," said the mother. "Was she in danger? There were twice as many boys here as girls. That was the worst part of it. And I was very embarrassed. I'm one of those stupid parents who went away and left their teenager at home."

But some lessons have been learned. "We have better communication with neighbors she can call in the middle of the night," she said. And she's more leery about taking trips off-Island and leaving their teenager at home.

But what about calling the police? The tenth-grade girl couldn't bring herself to do so, fearing that her peers would brand her a squealer.

Chief Toomey sympathizes with the peer pressure, but Edgartown police chief Paul Condlin said "kids have to cut their losses." The point is to call sooner rather than later.

"When you invite four and now there's 10 people," said Chief Toomey, that's when you call and say, "I just want help asking them to leave."

That's what a senior from Edgartown did last year when a spaghetti dinner with several friends turned into one of those spontaneous parties.

"I thought it was going to be cool," she said, "but it just happened all of a sudden, a whole bunch of people showed up."

Thinking quick, she went to the front porch, called the police and asked them to stick around to keep the convoy from stopping. To deflect any criticism, she told her peers that a neighbor must have called the police.

Chief Toomey said her department supports both kids and parents who make such a good decision. "We try to approach it gently," she said. Protocol calls for officers to conduct field sobriety tests.

"We don't want kids who are intoxicated running away," she said.

But the chief is careful to point out that the weekend party circuit should not be an occasion to "beat up on kids."

"This comes down to the responsibility of adults," she said.

And with new state laws on the book as of last year, it's much easier now to hold adults liable for what happens on their property when it comes to underaged drinkers.

"It's no longer just procuring" alcohol, she said. "It's allowing it to happen." Cape and Island assistant district attorney Lisa Edmonds said adults can face $2,000 in fines and up to a year of jail time if found guilty of violating the new law.

"I'm not saying you can't leave a 17-year-old at home, but you need some safety checks," said Chief Toomey. Enlist a friend to be not only on-call but checking in. Parents can let police and neighbors know they're going away and make it clear to teenagers that there shouldn't be any friends coming over.

"Kids don't like it because that's closing their network," said the chief.

But what's the alternative for teenagers? To the chief, the goal is keeping kids involved with adults as they leave the junior high grades and enter the high school.

A counselor at Martha's Vineyard Community Services, Lyndsay Famariss, is working with Island businesses, such as Mocha Mott's and Sodapops, willing to stay open late and offer a place for teens to hang out.

But those efforts will have to be sustained if they are to take hold.

"What are we doing in the lower grades to get kids to buy into another lifestyle?" asked Chief Toomey. "It's about money and work. That's notoriously where we have dropped the ball."