Cyberbullying is an emerging form of bullying that takes place through contemporary information and communication technologies. Building on past research on the psychosocial risk factors for cyberbullying in this age group, the present study assessed a theory-driven, school-based preventive intervention that targeted moral disengagement, empathy and social cognitive predictors of cyberbullying. Adolescents (N = 355) aged between 16 and 18 years were randomly assigned into the intervention and the control group. Both groups completed anonymous structured questionnaires about demographics, empathy, moral disengagement and cyberbullying-related social cognitive variables (attitudes, actor prototypes, social norms, and behavioral expectations) before the intervention, post-intervention and 6 months after the intervention. The intervention included awareness-raising and interactive discussions about cyberbullying with intervention group students. Analysis of covariance (ANCOVA) showed that, after controlling for baseline measurements, there were significant differences at post-intervention measures in moral disengagement scores, and in favorability of actor prototypes. Further analysis on the specific mechanisms of moral disengagement showed that significant differences were observed in distortion of consequences and attribution of blame. The implications of the intervention are discussed, and guidelines for future school-based interventions against cyberbullying are provided. Aggr. Behav. 42:114–122, 2016. © 2015 Wiley Periodicals, Inc.