Out-of-school programs can offer personalized and meaningful learning experiences that deepen students' knowledge and cater to their passions and interests, but it has been a painful reality that many such programs have been available only to students and families with privilege and resources. Karen Hammerness, Anna MacPherson, Preeti Gupta, Tramia Jackson, and Rachel Chaffee describe how the Science Research Mentoring Consortium in New York City gives students from underserved communities opportunities to engage in STEM activities alongside researchers at sites throughout the city. Students with a strong interest in and aptitude for science take classes after school or on weekends and conduct their own research with the support of mentors. The authors share the principles that undergird the program and that can be applied to similar mentoring partnership programs in other disciplines.