This study examined the feasibility of implementing an innovative theater-based after-school program, ‘Ready. Set. ACTION!’, to reach ethnically diverse and low-income children and their parents with obesity prevention messages. The study population included 96 children and 61 parents. Children were in fourth to sixth grade and 41% were overweight at baseline. Program impact was evaluated with a pre/post-randomized controlled study design, but a major focus was placed on the process evaluation conducted in the intervention schools. Intervention children and parents reported high program satisfaction and that they had made changes or intended to make positive changes in their behaviors due to program participation. However, few meaningful differences between the intervention and control conditions were found at follow-up. Thus, the combined process and impact evaluation results suggest that the intervention was effective in leading to increased awareness of the need for behavioral change, but was not powerful enough on its own to lead to behavioral change. From this feasibility study, we concluded that Ready. Set. ACTION! offers promise as a creative intervention strategy. The next research step may be to incorporate theater-based programs into more comprehensive school-based interventions, with both educational and environmental components, and evaluate program impact.