The NoTrap!(Noncadiamointrappola!)program is a school-based intervention, which utilizes a peer-led approach to prevent and combat both traditional bullying and cyberbullying. The aim of the present study was to evaluate the efficacy of the third Edition of the program in accordance with the recent criteria for evidence-based interventions. Towards this aim, two quasi-experimental trials involving adolescents (ageM= 14.91, SD= .98) attending their first year at different high schools were conducted. In Trial 1 (control group,n= 171; experimental group,n= 451), latent growth curve models for data from pre-, middle- and post-tests showed that intervention significantly predicted change over time in all the target variables (victimization, bullying, cybervictimization, and cyberbullying). Specifically, target variables were stable for the control group but decreased significantly over time for the experimental group. Long-term effects at the follow up 6 months later were also found. In Trial 2 (control group,n= 227; experimental group,n= 234), the moderating effect of gender was examined and there was a reported decrease in bullying and cyberbullying over time (pre- and post-test) in the experimental group but not the control group, and this decrease was similar for boys and girls. Aggr. Behav. 42:194–206, 2016. © 2016 Wiley Periodicals, Inc.