The question driving research on after-school programs is shifting from “do programs make a difference,” to “why are some programs effective while others are not?” This article draws on the work in this volume and related studies to suggest that there is an emerging consensus on the importance of staff-youth interactions as a determinant of program effectiveness. The commentary recommends that future research should continue to focus on understanding and improving program practices at the point-of-service. In doing so, two lines of inquiry seem promising. The first involves linking measures of changes in staff-youth interactions to changes in developmental outcomes. The second is to examine how policies or other interventions intended to improve program effectiveness affect the practices of line staff.