Background: Afterschool programs are promising arenas to improve youth physical activity (PA) levels. During the school year for 2012-2013, 5 elementary schools from a low-socioeconomic status (SES) school district in southern Colorado participated in evaluation of the afterschool program entitled Keep It Moving! (KIM). Methods: In this cross-sectional analysis we sought to evaluate the relationships among participant PA, teacher interaction, and lesson context during an unstructured afterschool PA program. Participants were third-fifth grade students enrolled in the KIM program at the 5 participating elementary schools and were assessed utilizing accelerometers and direct observation with the System for Observing Fitness Instruction Time (SOFIT). Results: Program participants wore the accelerometer 37.1?±?5.4?min?session[superscript -1.0] Approximately half of the time was spent in light PA (LPA) and 15.7?±?5.3?min?session[superscript -1] in moderate to vigorous PA (MVPA). Game play was positively associated with LPA and negatively associated with MVPA. When teachers did not promote PA with students there was a positive association with sedentary activity (SA) and a negative association with MVPA. Conclusions: Lesson context and teacher interactions may be important factors associated with PA intensity of afterschool PA programming. Future research should address whether structured PA curricula may improve quality of afterschool PA programming.