Self-report surveys were collected at 2 points in time over the course of 1 year from 7,299 ethnically diverse students (47.8 percent males, 52.2 percent females) in 5th, 8th, and 11th grades in 78 schools or community centers across Colorado. Results of ordinary least squares regression analyses indicated that self-esteem, school climate, and normative approval measured at Time 1 significantly predicted self-reported bullying perpetration 1 year later at Time 2, controlling for Time 1 bullying. Further, the effect of self-esteem on bullying perpetration was moderated by perceptions of school climate. When perceptions of school climate were negative (indicating poor school climate), high self-esteem predicted higher levels of bullying perpetration. In contrast, when perceptions of school climate were positive, high self-esteem predicted lower levels of bullying perpetration. The findings are discussed in terms of the need to consider individual and contextual factors and how they interact in understanding and preventing bullying in schools. (Published Abstract)