This study evaluated the impact of Supplemental Instruction (SI) at Morgan State University, an HBCU, on academic outcomes for underrepresented minority (URM) students in introductory STEM courses. SI is a peer-facilitated learning model aimed at reducing attrition rates and improving engagement and academic performance. SI Leaders facilitated weekly sessions for students in a supportive environment. Data from 104 STEM courses over five semesters showed that while SI did not significantly increase the number of passing grades overall, it positively affected grade distribution, particularly for students at risk of earning lower grades. This suggests that SI effectively supports students on the borderline between passing and failing, addressing educational equity for URM students. The study underscores SI's value in improving outcomes for struggling students in STEM fields at HBCUs, suggesting it could help bridge performance gaps and support retention and success among students from underrepresented groups.