This paper describes the development of the Toronto Anti-Bullying Intervention. The effectiveness of the Anti-Bullying Intervention was examined with quantitative and qualitative data gathered before and 18 months after its implementation. The results of this research confirm that bullying continues to be a pervasive problem in Toronto schools. There were some improvements in students' reports of bullying as assessed at the individual, peer, and school levels. Over the first 18 months of the program, children reported increased teacher interventions to stop bullying. More bullies indicated that teachers had talked to them, but there were no differences in the proportion of bullies or victims who had discussed their problems with parents. Fewer children indicated that they could join in a bullying episode following the intervention. There was an increase in the number of children who admitted to bullying, but a decrease in the number of children who had been victimized during the past five days. These inco...