This study examined classroom teachers’ involvement in a yearlong Comprehensive School Physical Activity Programs (CSPAP) implemented in one K-8 rural U.S. school district. Its purpose was to describe patterns of social interaction among teachers, administrators, and families associated with the intervention (i.e., social capital) and whether those interactions were associated with teachers’ program participation. Twenty-two teachers’ social capital as related to CSPAP activities was measured using a validated social capital instrument for teachers four times across one academic year and teachers reported their participation during wellness weeks. Regression and RM-ANOVA were used to analyse the data. Teacher social capital was significantly positively related to implementation of physical activity breaks. The more often a classroom teacher spoke with someone else, the greater the likelihood of that teacher leading a physical activity break. This study provides evidence for the importance of social capital in supporting the implementation of CSPAPs.