Understanding how to foster belonging and ensure equitable engagement in STEM fields for diverse students is a critical need in education today. Despite substantial growth in the STEM workforce (Bureau of Labor Statistics, 2023; NSF, 2023a), there remain persistent gender and racial/ethnic gaps in students’ access to advanced STEM education, which, in turn, affects college STEM pathways and workforce entry (NSF, 2023c; NSF, 2024). Grounded in the belongingness hypothesis (Baumeister & Leary, 1995) and vulnerability hypothesis (Hughes et al., 2015), this dissertation explores the role of belonging across three functions—outcome, mediator, and predictor—using a large, longitudinal sample of racially and ethnically diverse high school students.

This research employed three complementary analyses. Study 1 investigated demographic and contextual predictors of 12th grade belonging in math and science classrooms, identifying racial/ethnic and gender patterns in belonging and highlighting the influential role of perceived ingroup representation for belonging in math classrooms. Study 2 examined whether belonging mediated the relationships between demographic characteristics and advanced math course taking, finding that while math belonging partially explained some racial/ethnic disparities in course taking, the indirect effect was modest. Study 3 assessed the predictive power of 9th-grade math and science belonging on STEM persistence, indicating that early feelings of belonging in math were significantly associated with students’ later engagement with STEM, whereas science belonging had no significant predictive effect. Together, these studies underscore the multifaceted role of belonging in shaping STEM engagement for high school students, particularly for historically underrepresented groups. Findings reveal that belonging in math settings is especially impactful and that representation of demographically similar peers in math classrooms may be crucial for fostering belonging in these contexts. This work highlights the need for tailored interventions that support belonging as early as high school to address demographic disparities in STEM engagement and persistence, ultimately contributing to a more diverse and inclusive STEM workforce.