Organized school activities and community programs have the potential to provide key supports and opportunities for youth, especially for low-income youth who are in the greatest need of additional supports (Furstenberg et al., 1999). Calls have been made to identify potential mechanisms of development that link activity participation to youth outcomes. The extent to which youth are autonomously motivated about participating in their activity, in other words, how self-determined they are in regulating their behavior (Deci & Ryan, 2002), may be one such mechanism. There are three key features of activity participation that may promote autonomous motivation: the type of activity a young person participates in (e.g., sports vs. academic clubs), connectedness to adults in their program, and the duration or length of their participation. In addition, engagement in reflective practices may assist youth in drawing out the meaning embedded in their activity experiences, thus enhancing autonomous motivation. The Afterschool Community Empowerment (ACE) Project was conducted in the fall of 2009 with 1198 students (56% White, 31% Black/Hispanic/Latino, and 40% iii participating in the free/reduced lunch program) attending Binghamton High School in Binghamton, New York. A school-wide paper-pencil survey including an activity participation inventory and items measuring youth outcomes was used to collect selfreport data. Current activity participants (72% of total sample) also answered questions about program processes and proximal outcomes. Overall results from this investigation showed that: a) there was a higher proportion of high SES youth who reported more favorable outcomes (e.g., well-being) among activity participants vs. non-participants, b) youth with different characteristics (e.g., gender) differed in the types of activities they participate in, how connected they feel to adults, and their participation duration (e.g., high SES White youth and boys had greater odds of participating in sports), c) participation in sports and performing and fine arts programs were associated with significantly higher autonomous motivation vs. academic clubs and faith-based/community programs, d) connectedness to adults in programs is the activity participation feature with the strongest positive relationship to autonomous motivation (parental support moderates this relationship), e) youth who reported high connectedness and longer duration reported the highest autonomous motivation, f) autonomous motivation was shown to be positively associated with three of six indicators of well-being (i.e., life satisfaction, positive affect, psychological resilience), g) six reflective patterns about program experiences were identified, and certain participant characteristics were associated with greater odds of engagement in a particular reflective pattern, and h) youth who engage in a moderate, well-balanced set of reflective practices (vs. are not reflective at all, for example) report significantly higher autonomous motivation. Implications for policy and practice, the limitations of this study, and recommendations for future research are discussed. iv