Issues addressed: Improving children's opportunities for and participation in physical activity at out-of-school hours (OOSH) care. Methods: A needs assessment, 12-month implementation and evaluation were conducted. Strategies included feedback and support to improve physical activity programs and policies; staff training; resource distribution; and grants to disadvantaged services. Strategies were developed in partnership with an advisory committee from the OOSH sector. Physical activity policies, the types of after-school activities offered and children's participation in these activities were evaluated before and after implementation. Results: Statistically significant improvements were seen in the proportion of moderate or vigorous activities programmed each week. Children's participation showed a significant shift from lower to higher-intensity activities. Improvements were also seen in the number of services with planned physical activity programs and physical activity policies. Conclusion: The OOSH sector is an effective setting for promoting children's physical activity.