Framed by self-determination and identity development theories, this study examined the process through which participating in a community-based service-learning project supported high school students' feelings of autonomy, competence and relatedness, and how these feelings were related to students' intentions for doing more service in the future. The goals were to understand 1) the task and time related variations in students' reports of autonomy, competence and relatedness, and 2) whether these task and time related variations differed for youth who did service voluntarily compared to those who did service to fulfill a requirement. Results showed increases in autonomy, competence and relatedness over the course of the project, as well as task-related variations in these feelings. Competence and relatedness positively predicted internalized reasons for future service. Internalized reasons positively predicted strong intentions for future service. Required and voluntary service participants reported similar levels of autonomy, competence and relatedness, as well as similar reasons and intentions for future service. Implications provide insights into designing service programs for adolescents' optimal psychosocial development during out-of-school time.