Social exclusion is a serious social problem. Not "fitting in" at school may be an experience that can scar children psychologically for life. This is unsurprising since being part of the "in crowd" (i.e. accepted in-group members) is extremely important to children and adolescents. Being rejected by one's peers can cause an increase in antisocial behaviour, deviance, aggression, lowered intellectual performance, self-defeating behaviour and a series of other maladaptive responses. Thus, an important social task that children face is to work out when their own and others' behaviour contravenes social norms, and to decide how to respond when such norms are contravened. Namely, they need to form attitudes towards nonconformity. Societal and interpersonal responses to deviance may focus primarily on the "problem" child and his or her personal or family relationships. However, the authors argue that such focus may miss a significant dimension, namely that when and how a behaviour is defined as "deviant" is also part of a wider peer group process that defines and defends group norms and boundaries. In this paper, the authors consider how the intergroup context (i.e. perceived relations between one's own and other social groups) and socio-cognitive development (i.e. the emergence of social-cognitive abilities) affects school children's reactions to non-conformists in their peer group.