BoSTEM, implemented by United Way of Massachusetts Bay and Merrimack Valley and Boston Afterschool and Beyond, is a network of STEM-focused after school programs in the Boston area that provide high-quality science, technology, engineering, and math (STEM) opportunities to Boston middle school students. Through an innovative citywide coalition of nonprofits, schools, researchers, and industry partners, BoSTEM aims to close the opportunity and achievement gap for youth traditionally underrepresented in STEM through exciting, hands-on learning and career mentorship. The BoSTEM impact evaluation used a quasi-experimental design (QED) to examine the effect of BoSTEM on social-emotional learning skills. The study examined outcomes for students in school years 2020-21 and 2021-22. Outcomes for BoSTEM students were compared to a sample of students who participated in business-as-usual afterschool STEM programs that did not receive the BoSTEM structure of support that included performance feedback, coaching, and professional development opportunities. Findings show there was no significant difference between BoSTEM and comparison students in development of social-emotional learning skills. Challenges with data collection and recommendations for future evaluation studies are discussed.