In order to provide greater clarity and direction for practice in youth violence prevention, this article suggests that program evaluations focus not only on outcomes, but also on factors that influence outcomes. As illustrated with findings from the Metropolitan Area Child Study (MACS), evaluations that do not consider specific variables that affect outcomes may conclude that a program is ineffective for all children when it was actually effective for some of the children. In the MACS example, the full intervention was effective only for younger, more aggressive children in schools with greater resources; however, when clinical significance was considered, the program was effective in reducing the aggression level of the most aggressive youth to normative levels regardless of school resources. It may be that school resources are important for implementation overall; within a school, however, a teacher with one or two highly aggressive children might also be motivated to implement an intervention that compensates for limitations on school resources. Given the diversity of outcomes due to varying conditions and the characteristics of individuals involved in a program to prevent youth violence, this article proposes that evaluators focus on second-level evaluation studies in order to assess the effectiveness of interventions across different settings and for different groups involved in the intervention. In deciding what program to use in an attempt to prevent youth violence, program selection must determine whether the program worked with the type of youth being targeted for a current intervention and whether the settings were similar. 44 references