Afterschool programs (ASPs) have become increasingly recognized as a key context to support youth daily physical activity (PA) accrual. Using Self-Determination Theory (SDT) as a framework, this study examined staff perspectives on the strengths and barriers within under-resourced ASPs for establishing a social-motivational climate for encouraging and supporting youth PA. Analysis of semi-structured staff interviews (28 staff; 7 ASPs) indicated that staff had knowledge and value for establishing a PA-supportive motivational climate. However, the feasibility of implementing PA curricula was identified as challenging across programs. Findings suggest increased need for staff training and supports to provide a PA climate that meets the developmental needs/interests of all youth, with particular attention toward increasing the PA of girls and older program youth. Furthermore, striking an appropriate balance between PA and other competing program demands (e.g., academics) will be required to optimize on the effectiveness of PA program components.