Childhood overweight and obesity disproportionately affect low-income communities. Most school-based health promotion efforts occur during the school day and are limited in scope. This study evaluated the effectiveness of an after-school program among 3rd-5th graders (n=121; 73% 8 to 9 years old; 57% female; 60% Asian) at eight study sites (four intervention, four comparison). After-school staff were trained on implementing the Catch Kids Club Curriculum on nutrition and physical activity. Data were collected on students' nutrition and physical activity knowledge and behavior, and their height and weight measurements. Using Stata 10.1/SE, cross-lagged regression models assessed changes over time. Results showed a reduction in overweight and obesity (defined as body mass index >85th percentile for age and sex) among children in the intervention group, but mixed results regarding diet and physical activity knowledge and behavior. Enhancing after-school physical activity opportunities through evidence-based programs can potentially improve overweight and obesity among low-income children.