The present study evaluates the effect of an intervention program on the reduction of bullying and victimization in schools with a sample of 239 students aged 10-16 years old in Rome, Italy. The program deals with bullying and violence. It consists of three videos and a booklet that help students to develop the social cognitive competence skills to understand the negative consequences of aggressive behavior. The intervention was evaluated using an experimental design with pre-test and post-test analyses. Students were randomly allocated to experimental or control classes. Students completed a self-report questionnaire in which they were asked to indicate on a 5-point scale how often they were victimized or bullied others. Victimization and bullying were assessed by using questions about specific types of actions, a composite measure of victimization and bullying, and a single question about victimization and bullying in general. Results showed that the program worked best for older students, but not for younger ones who in some cases reported an increased level of victimization after the intervention. For older students there was a decrease in victimization according to the sum of types of behavior for the experimental group, but an increase for the control group. The same result was found for direct victimization, having belongings stolen, and being called nasty names. Therefore, the program seemed to be beneficial for older students but possibly damaging for younger students. It is suggested that the program could have worked better with older students because of the cognitive skills it required. Younger students could have reported higher levels of bullying after the intervention because they became more sensitized to the topic of bullying. © 2004 Wiley-Liss, Inc.