Tested and effective approaches are available to prevent mental, emotional, and behavioral problems in youth, but such approaches are underused. Communities That Care (CTC) is a coalition-based strategy that aims to increase the use of tested and effective programs by combining the use of scientific evidence and stakeholder consensus to support the community adoption of a scientific approach to preventing mental, emotional, and behavioral problems in youth. A community-randomized trial of CTC was conducted with a sample of 24 communities matched in pairs and assigned randomly to a control or an intervention condition. The findings demonstrate that CTC significantly increases the community-wide adoption of a science-based approach to prevention. Using a meta-analysis technique, this study shows that despite uniformly high-fidelity implementation of CTC in intervention communities, the effect of CTC on the adoption of a scientific approach to prevention varies significantly across the 12 community pairs. Understanding the extent of variation in the effect of CTC on adopting a science-based approach to prevention lays a foundation for identifying aspects of coalition structure, functioning, or capacity that not only may help explain variation in adoption, but may in turn be targeted to strengthen the effect of CTC on the adoption of a science-based approach to prevention within communities.