When people are rejected by peers, they often lash out. In children, that aggression occasionally takes horrifying directions, leading to school shootings or other deadly acts. Researchers in the Netherlands found that some children are more likely than others to lash out in response to acute peer rejection: children who already feel like outcasts.

"It was inspired by the fact that we had these school shootings and wondered what the most important feature of these kids could be," says Albert Reijntjes of Utrecht University, who cowrote the study with five other psychological scientists. "In discussing it with colleagues, the alienation concept came up; maybe there is something to alienation that increases aggression."

The researchers recruited students in two or three classes at each of three Dutch schools; 121 students aged 10 to 13 took part in the study. Each child was told they were playing an Internet contest called "Survivor" -- a fake contest for the study. Each child completed a personal profile to be allegedly uploaded to the website alongside their picture. Then they were given time to look over the feedback they received from eight judges, children from other schools. Some of the children received mostly positive feedback; some had mostly negative feedback, like, "This person does not seem fun to hang out with."

Finally, the child had a chance to choose how much money each judge would get, and to write comments about the judges.

Students who had been rejected were more likely to act aggressively toward judges -- taking away money from them and/or writing comments like "this person is fat and mean." They were even more aggressive if they'd scored high on a measure of alienation -- agreeing with statements like, "Hardly anyone I know is interested in how I really feel inside."

The results are published in Psychological Science, a journal of the Association for Psychological Science.

The experiment ended with a thorough debriefing session, where the researchers explained the project and that the judges and their mean comments were fake. To round it off, "We talk at length about a recent positive social experience they have had and they get a present," Reijntjes says. "So far, that has always been successful in not getting crying kids."

"When you're an outcast, you're more likely to lash out aggressively when faced with bad peer experiences," says Reijntjes. "Although we examined "normal" aggression in a community sample, the findings shed light on factors involved in the more dramatic acts of aggression such as school shootings." Maybe part of the solution is to help children not to feel like outcasts; he says it could be useful to look out for children who feel alienated and design interventions that help them feel part of the group.