Middle school students’ experiences at after-school programs were compared as they participated in different types of activities and with different social partners. The students (N = 165) attended eight programs in three Midwestern states. A total of 1,596 experiences were randomly sampled using the Experience Sampling Method (ESM) during 1 week in the fall of 2001 and 1 week in the spring of 2002. Student engagement was conceptualized as the simultaneous experience of concentration, interest, and enjoyment. Students reported high levels of engagement while participating in sports activities and arts enrichment activities at the after-school programs, and low levels of engagement while completing homework at programs. They reported being more engaged in activities involving both adults and peers than activities with peers only. Concentrated effort, intrinsic motivation, and positive and negative mood states were also compared by program activities and social partners. Findings about participants’ subjective experiences and engagement in specific program activities have implications for understanding after-school programs as a context for youth development.