Girls are mean. Don't believe that? Just ask Lara. On her first day at Challenger Middle School, the sixth-grader wore sweat pants and a T-shirt. An older girl gave her a disapproving look.

"Don't ever wear (sweat pants) again," Lara remembered the girl telling her. "They're not in. Wear jeans or something."

Soon the most popular girls were giving Lara rules on nearly every aspect of her life - her clothes, food, friends.

When Lara balked, they called her a "loser." They harassed her. They pushed her. They ignored her. They were mean.

"Welcome to middle school," Lara, 12, says sardonically as she retells her first year of adolescence.

What Lara sees as the normal school routine, experts see as bullying. The tendency for schoolgirls to control each other and others through gossip, cliques and exclusion isn't just part of growing up, some experts say. It's got a name: relational aggression.

It's when girls use their intimacy - friendships, relationships - to manipulate and intimidate others.

Researchers and experts have turned their attention to female bullies and have written books, magazine articles and studies on the subject.

They point to what some experts call a glaring omission in anti- bullying programs used in schools nationwide.

Most anti-bullying programs, including ones used in Colorado schools, focus primarily on physical aggression - the kind when big boys stuff little boys into lockers.

But it's a mistake to ignore girls' style of bullying, says Stephen Leff, a psychologist at Children's Hospital of Philadelphia and principal investigator in a study that looked at bully- prevention programs in schools nationwide. That's because relational aggression can be more harmful, vicious and have deeper and more lasting effects than any schoolyard fistfight.

"Intimacy in girls' friendships is extremely important, so a manipulation of that can really have a profound effect," said Leff.

Some experts say relational aggression can lead to suicide, drugs and eating disorders in girls.

"Girls need to be held responsible for the things they do that bring them all down," said Rosalind Wiseman, author of "Queen Bees and Wannabes: Helping Your Daughter Survive Cliques, Gossip, Boyfriends, and Other Realities of Adolescence."

Examples of bullying

A few students at Challenger Middle School, on the city's northeast side in Academy School District 20, agreed to talk about girl bullying only if their last names weren't used. They didn't want anyone in school to know they were talking about it to outsiders.

"They're vicious," said a 12-year-old sixth-grader at Challenger. "They can come up to you all nice, but then they will take something you tell them and (use it against you)."

And girls don't just bully other girls. They bully boys as well.

Take what happened to Jonathan, another Challenger sixth-grader. About a week ago, a girl in Jonathan's class, a friend, called him. The girl urged him to talk about another girl he liked. While Jonathan professed his love, he heard giggling.

"Someone else was there on the telephone," said Jonathan, 12. "It was horrible. I just hung up."

Girl bullying comes in many forms: Using three-way calling to catch someone spilling their deepest, darkest secrets, creating Internet "slam books" to label a girl a slut, whore or tramp, shunning a girl because she wears sweat pants instead of capris. Girls use intimate knowledge to needle someone else.

"Girls bully in more sophisticated and complex ways, (than boys do)," said Wiseman, who also runs The Empower Program. Based in Washington, D.C., Wiseman's program teaches girls how to cut out their aggression and avoid bullying.

Experts believe girls bully like this because, in general, they're less physical than boys. Yet girls still need to express aggression.

Leff says schools mistake this behavior by girls as just part of childhood.

"It's much more subtle when someone bullies through social or relational aggression," he said. "One person at the school may not see it, and when they do, they may feel it's not as serious as physical aggression."

These type of mind games have been going on among schoolgirls for decades. What's the harm? Plenty, says Wiseman.

It can be deadly. In Canada, a 16-year-old girl was found guilty of threatening and harassing a classmate who later committed suicide. In Colorado Springs, a 13-year-old girl committed suicide in 1999 after she was bullied by middle schoolers, many of them girls, her parents said.

But the harm can be felt in small ways, too. Lara has few "popular" friends at her new school.

"You just feel so isolated," she said.

There's also harm for girls who perpetuate this behavior, said Wiseman.

Through her program, Wiseman has talked to hundreds of so-called popular girls. She noticed many of them felt powerless.

"(Bullying) is about girls wanting social status," Wiseman said. "The more important social status is to their sense of self, the more important it is for them to achieve and maintain it."