Contrary to the findings from previous reviews we found little support for the general notion that greater amounts of participation in afterschool programs was related to academic, behavioral, or socio-emotional outcomes. However, some relationships did emerge depending on how participation was conceptualized and measured, and the methodology used to assess the relationship between participation and outcomes. For example, some benefits occurred when participants with high levels of participation were compared to non-participants, not when they were compared to other program participants. Several suggestions are offered to improve future research on the relationship between aspects of participation and developmental outcomes.