The role of context in the development of child aggression was studied. The effects of peer aggregation and group composition on aggression development in intervention contexts and classroom contexts were compared using 71 elementary school children. We hypothesized that, due to peer group effects, group-trained children would benefit less from a social skills intervention program than individually trained children. We further hypothesized that children who transferred from special to regular education would show a change toward less aggression. This was hypothesized because of the relatively fewer accounts of negative peer-group effects in regular education. The results show that the social skills intervention program did not have differential effects for group-trained versus individually trained children. However, a change toward less aggression was found in children who transferred from special to regular education. We suggest that interventions toward decreasing child aggression might be more fruitful if the social context in which the children operate daily is considered.