Clinicians and training programs strive to implement evidence-based practices and manualized treatments with fidelity. However, the constraints of a local setting may limit the extent to which this is possible. In the current study, an adapted model of an evidence-based social-emotional learning small group curriculum, the Incredible Years Children's Small Group Training Series (Webster-Stratton, 2004), was implemented and evaluated in an elementary school setting. Results of the study demonstrated statistically significant decreases in problem behaviors and intensity of problem behaviors, as rated by teachers. Teachers also reported improvement in classroom behavior, emotion regulation, problem-solving, and friendship skills, as well as a high overall level of satisfaction with the intervention itself. Discussion of the results includes a review of the strengths and limitations associated with outcome research in a naturalistic setting, suggestions to consider when adapting evidence-based programs, and recommendations for future research.