While numerous studies have highlighted the consequences of exclusion in STEM, fewer studies have empirically tested the benefits of inclusion in peer relationships. We focus on the impact of having cross-racial or cross-gender study partners among one's close friends in a national sample of 408 STEM majors. Using structural equation modeling, we examined the direct and indirect relationships between having diverse study partners, key background and college experience variables, and college GPA. We identified a significant positive relationship, both direct and indirect, between studying with a close friend of a different race and GPA. We also found that having a cross-gender study partner is positively linked to organizing study groups and study-faculty interaction, which in turn improves GPA. However, Black students were less likely to have either cross-racial or cross-gender study partners among their close friends. We discuss implications for equity and the need to encourage positive intergroup relations in STEM.