Over the past ten years there has been an increasing emphasis on taking preventative approaches to reduce bullying and victimization in schools (Berger, 2007). In the wake of the horrifi c school shootings in Columbine and other areas in the United States, it is not surprising that schools have been focusing upon bullying prevention and social skills promotion in order to try to prevent future acts of violence and to create safer and more productive environments for youth (Modzeleski, 2007). A number of bullying prevention programs have been designed to promote children’s social skills, empathy and perspective taking skills, and problem-solving skills and have demonstrated some positive eff ects (Frey, Nolan, Van Schoiack-Edstrom, & Hirschstein, 2005; Leff et al., 2009; Lochman & Wells, 2004). At the same time, many bullying prevention programs that are being implemented across the country still lack empirical support and/or are not currently implemented or evaluated systematically (Leff , Power, Manz, Costigan, & Nabors, 2001; Perepletchikova, Treat, and Kazdin, 2007). Most notably, there is an increasing need to develop, validate, and utilize community responsive outcome measures in order to more successfully monitor how interventions are carried out and received within the schools (Leff , Power, Costigan, & Manz, 2003). Th is chapter will provide a summary of the most common classes of outcome measures being used to evaluate schoolbased bullying and aggression prevention programs, and a detailed description of their strengths, limitations, and recommended uses. In addition, the chapter will also discuss the importance of integrity monitoring assessment in bullying prevention programming (Leff , Hoff man, & Gullan, 2009). Finally, the chapter will conclude with a review of several important considerations in assessing outcomes of school-based aggression and/or bullying prevention programming.