Flexibility, opportunities for exploration, and a focus on 21st century skills make out-of-school time (OST) programs an ideal environment for authentic learning in science, technology, engineering, and mathematics (STEM; Committee on STEM Education, 2013; Noam & Shah, 2014). In addition, because OST programs serve significant populations of young people who are underrepresented in STEM, they may be able to reduce the opportunity gap for these youth and help to enhance youth learning and engagement. This article presents one approach to the design and development of professional learning resources for OST educators as they implement a high-quality STEM curriculum. The resources were developed as a team, based on research into the STEM professional development needs of OST practitioners, and they constitute a form of self-driven professional learning. The tiered system of professional development resources developed may guide other OST STEM programs toward providing the professional learning resources OST educators need to facilitate quality instruction.