So far this year, at least two teenage girls have committed suicide after repeatedly being attacked and insulted by a group of classmates. Being the target of a clique, or having a string of enemies, is especially treacherous, researchers say. And while suicide remains rare, antagonism is pervasive: studies have found that 15 to 40 percent of elementary schoolchildren have been involved in at least one such relationship — and that the rate in middle school and high school, where exclusion and gossip run highest, ranges from 48 to 70 percent.

Yet psychologists have found shortcomings in this early work. For one thing, most children (and adults) who have had rivals, antagonists or enemies are doing fine, thanks. For another, the results have been warped by a phenomenon called peer rejection: a small group of children are so different from their peers that they suffer far more than their share of bullying.

In a review of these types of studies in the current issue of the journal Developmental Psychology, Noel A. Card, a psychologist at the University of Arizona, corrected the combined results for peer rejection. “Once you factor out peer rejection,”” he said in an interview,, “the effects of antipathetic relationships on adjustment are pretty slight.”

This will come as small comfort to children and adolescents in the trenches, who may be swimming in foul text messages, threats or humiliating gossip. The sting is especially deep when good friends turn against one another.

In an earlier study, titled “We Were Friends, but ...,” Dr. Card found that soured friendships were a common, and particularly intense, form of mutual antagonism. One participant described what happened after a friend left her at a party, going home with someone else without saying anything: “The next day I confronted her, and we got into a fight and suspended from school. That’s when she started spreading rumors.”

Ms. Shapiro’s fight with her former friend was partly for show. The stronger girl pretended to hit her — and told her to run away holding her face, for the benefit of the other tough kids watching. It was terrifying nonetheless. “I ran all the way home,” she said. “All through high school I was scared of her, and we didn’t talk. I just avoided her.”

Most hostile ex-friends do the same, Dr. Card found, and the hostility does not escalate. Moreover, the weak link between negative relationships and development represents an average: for every person with a profoundly bitter rival or enemy, there are others with milder antagonisms, which may provide opportunities for social and emotional development.