In 2 studies the authors examined knowledge and social information-processing mechanisms as 2 distinct sources of influence on child aggression. Data were collected from 387 boys and girls of diverse ethnicity in 3 successive years. In Study 1, confirmatory factor analyses demonstrated the discriminant validity of the knowledge construct of aggression beliefs and the processing constructs of hostile intent attributions, accessing of aggressive responses, and positive evaluation of aggressive outcomes. In Study 2, structural equation modeling analyses were used to test the mediation hypothesis that aggression beliefs would influence child aggression through the effects of deviant processing. A stronger belief that aggressive retaliation is acceptable predicted more deviant processing 1 year later and more aggression 2 years later. However, this latter effect was substantially accounted for by the intervening effects of deviant processing on aggression.