The current study tests a social-cognitive model of bystander responses to bullying in an attempt to better understand why bystanders respond as they do. Three forms of bystander responses were predicted by adult and friend responses to bullying and the bystander’s reasons for intervening. The present study involved 326 children from grades 4-8 who completed the PREVNet Assessment Survey, a novel wide-ranging measure of bullying phenomena. Sound psychometric properties were found for the four measures used in the present study. In elucidating the effects of social context, the differential impact of adult and friend responses on bystander responses was examined. Results indicate that friends are more influential than are adults in predicting bystander responses. Further, results of serial multiple mediation analysis generally support a social-cognitive model, suggesting that social context impacts intervention reasoning, which in turn, impact bystander responses. Implications for future research and policy are discussed. / SSHRC Joseph-Armand Bombardier CGS Master's Scholarship