This longitudinal study investigated the effects of witnessing violence on committing violence among diverse urban middle school students (11-15 years old) over a 1-year period (N=1,599). It examined parent support and prosocial cognitions as moderators that might interact with one another in buffering adolescents from the effects of witnessing violence. The study also explored gender and ethnicity differences across these protective processes. According to the results, both average and high levels of parent support may offer male adolescents who witness violence protection against committing subsequent acts of violence. Adolescent females who witness violence appear to be uniquely protected from committing acts of violence if they have highly prosocial cognitions. Applications to resilience and competency models are discussed.