A good relationship with a teacher mitigates against a child expressing aggression and being the target of aggression at school, researchers in Canada say. Study leader Mara Brendgen of the University of Quebec at Montreal studied 217 Canadian identical and fraternal twin pairs at age 7. The twin pairs had different teachers and different classmates. Classmates rated the twins\' level of aggressive behavior and the extent to which they were victimized by peers, Brendgen said. The twins\' teachers rated the quality of their relationship with each twin. Genetic effects on aggression were estimated by comparing the similarity in behaviors of identical and fraternal twin pairs, Brendgen said. The study, published in the journal Child Development, found children genetically vulnerable to being aggressive were more likely to be victimized by their classmates than others, but these children were protected from acting aggressively and being the target of other children\'s aggression if they had a very good relationship with their teacher. \"Aggressive behavior in middle childhood is at least partly explained by genetic factors, but genetic influences on behavior usually don\'t operate independently of environmental influences,\" Brendgen said in a statement. \"Our study found that a good relationship with the teacher -- a relationship that was warm and affectionate and involved open communication -- can protect genetically vulnerable children from being aggressive and, in consequence, from becoming the target of other children\'s aggressive behavior.\"