Afterschool programs (ASPs) have potential to provide children moderate to vigorous physical activity (MVPA). The availability and types (e.g., free play or organized activities) of physical activity opportunities, their structure (e.g., presence of lines, elimination games), and staff behaviors (e.g., encouragement, engaged) can influence children’s MVPA. This study explored these factors in 20 ASPs serving over 1,700 elementary-age children. The occurrence, types, and structure of physical activity opportunities, and staff behaviors were collected via the SOSPAN (System for Observing Staff Promotion of Physical Activity and Nutrition). A total of 4,660 SOSPAN scans were completed across 63 complete program days (1,733 during physical activity opportunities). Physical activity opportunities were observed on 60 program days across all 20 sites, with 73% of those opportunities classified as free play. ASPs scheduled an average of 66.3 minutes (range 15-150 minutes) of physical activity opportunities daily. Games played included basketball, tag, soccer, and football. Staff rarely engaged in physical activity promotion behaviors, and the structure of organized games discouraged MVPA. For example, staff verbally promoted physical activity in just 6.1% of scans, while organized games were more likely to involve lines and elimination. Professional development training may enhance staffs’ physical activity promotion and the structure of activity opportunities.