This study assesses the association between cognitive schemas of justification of violence, grandiosity and abuse, and reactive and proactive aggressive behavior, and whether this association is mediated by social information processing (SIP). For this purpose, a sample of 1371 adolescents (638 girls and 580 boys) completed measures of cognitive schemas, SIP, and Reactive-Proactive Aggression. The results showed that the cognitive schemas of justification of violence and narcissism are more relevant for proactive aggression, whereas the abuse schema is more relevant for reactive aggression. SIP mediated particularly the association between cognitive schemas and reactive aggression. Each cognitive schema was shown to be associated with some particular SIP component: justification of violence and abuse with the component of interpretation, and narcissism with the experience of anger. Moreover, the abuse schema was negatively associated with the selection of aggressive responses. Lastly, a general model of paths between schemas, SIP, and aggression was found to be quite similar for boys and girls, although the former scored higher in proactive aggression, partly because of their higher scores in the justification of violence and narcissism schemas.