Researchers following in Bjorkqvist's footsteps noted that up to the age of 4 girls tend to be aggressive at the same rates and in the same ways as boys -- grabbing toys, pushing, hitting. Later on, however, social expectations force their hostilities underground, where their assaults on one another are more indirect, less physical and less visible to adults. Secrets they share in one context, for example, can sometimes be used against them in another. As Marion Underwood, a professor of psychology at the University of Texas at Dallas, puts it: ''Girls very much value intimacy, which makes them excellent friends and terrible enemies. They share so much information when they are friends that they never run out of ammunition if they turn on one another.''

In the last few years, a group of young psychologists, including Underwood and Nicki Crick at the University of Minnesota, has pushed this work much further, observing girls in ''naturalistic'' settings, exploring the psychological foundations for nastiness and asking adults to take relational aggression -- especially in the sixth and seventh grades, when it tends to be worst -- as seriously as they do more familiar forms of bullying. While some of these researchers have emphasized bonding as a motivation, others have seen something closer to a hunger for power, even a Darwinian drive. One Australian researcher, Laurence Owens, found that the 15-year-old girls he interviewed about their girl-pack predation were bestirred primarily by its entertainment value. The girls treated their own lives like the soaps, hoarding drama, constantly rehashing trivia. Owens's studies contain some of the more vivid anecdotes in the earnest academic literature on relational aggression. His subjects tell him about ingenious tactics like leaving the following message on a girl's answering machine -- Hello, it's me. Have you gotten your pregnancy test back yet?'' -- knowing that her parents will be the first to hear it. They talk about standing in ''huddles'' and giving other girls ''deaths'' -- stares of withering condescension -- and of calling one another ''dyke,'' ''slut'' and ''fat'' and of enlisting boys to do their dirty work.

Relational aggression is finding its chroniclers among more popular writers, too. In addition to Wiseman's book, this spring will bring Rachel Simmons's ''Odd Girl Out: The Hidden Culture of Aggression in Girls,'' Emily White's ''Fast Girls: Teenage Tribes and the Myth of the Slut'' and Phyllis Chesler's ''Woman's Inhumanity to Woman.''

In her book, the 27-year-old Simmons offers a plaintive definition of relational aggression: ''Unlike boys, who tend to bully acquaintances or strangers, girls frequently attack within tightly knit friendship networks, making aggression harder to identify and intensifying the damage to the victims. Within the hidden culture of aggression, girls fight with body language and relationships instead of fists and knives. In this world, friendship is a weapon, and the sting of a shout pales in comparison to a day of someone's silence. There is no gesture more devastating than the back turning away.'' Now, Simmons insists, is the time to pull up the rock and really look at this seething underside of American girlhood. ''Beneath a facade of female intimacy,'' she writes, ''lies a terrain traveled in secret, marked with anguish and nourished by silence.''

Not so much silence, anymore, actually. For many school principals and counselors across the country, relational aggression is becoming a certified social problem and the need to curb it an accepted mandate. A small industry of interveners has grown up to meet the demand. In Austin, Tex., an organization called GENaustin now sends counselors into schools to teach a course on relational aggression called Girls as Friends, Girls as Foes. In Erie, Pa., the Ophelia Project offers a similar curriculum, taught by high-school-aged mentors, that explores ''how girls hurt each other'' and how they can stop. A private Catholic school in Akron, Ohio, and a public-school district near Portland, Ore., have introduced programs aimed at rooting out girl meanness. And Wiseman and her Empower Program colleagues have taught their Owning Up class at 60 schools. ''We are currently looking at relational aggression like domestic violence 20 years ago,'' says Holly Nishimura, the assistant director of the Ophelia Project. ''Though it's not on the same scale, we believe that with relational aggression, the trajectory of awareness, knowledge and demand for change will follow the same track.''

Whether this new hypervigilance about a phenomenon that has existed for as long as most of us can remember will actually do anything to squelch it is, of course, another question. Should adults be paying as much attention to this stuff as kids do or will we just get hopelessly tangled up in it ourselves? Are we approaching frothy adolescent bitchery with undue gravity or just giving it its due in girls' lives? On the one hand, it is kind of satisfying to think that girls might be, after their own fashion, as aggressive as boys. It's an idea that offers some relief from the specter of the meek and mopey, ''silenced'' and self-loathing girl the popular psychology of girlhood has given us in recent years. But it is also true that the new attention to girls as relational aggressors may well take us into a different intellectual cul-de-sac, where it becomes too easy to assume that girls do not use their fists (some do), that all girls are covert in their cruelties, that all girls care deeply about the ways of the clique -- and that what they do in their ''relational'' lives takes precedence over all other aspects of their emerging selves.

After her class at the National Cathedral School, Wiseman and I chat for a while in her car. She has to turn down the India Arie CD that's blaring on her stereo so we can hear each other. The girl she had stayed to talk with after class is still on her mind, partly because she represents the social type for whom Wiseman seems to feel the profoundest sympathy: the girl left behind by a newly popular, newly dismissive friend. ''See, at a certain point it becomes cool to be boy crazy,'' she explains. ''That happens in sixth grade, and it gives you so much social status, particularly in an all-girls school, if you can go up and talk to boys.