This study employed a mixed-methods explanatory sequential design to provide a richer understanding of the relationship between peer mentoring and the academic success of students in STEM gatekeeper courses. The purpose of this study was to identify the factors contributing to the students' retention and persistence in a STEM program at an HBCU by obtaining quantitative survey data from senior level STEM students and then following up with purposefully selected individuals to explore those results in a qualitative interview. This study also determined if there were any differences in the reporting of gatekeeper course challenges of underrepresented STEM participants in a peer mentoring program in contrast to non-participants. This study also explored if participating in a peer mentoring program promoted academic and social integration at the university. The years examined were 2019 to 2022. The peer mentoring program was a component of a statewide STEM minority initiative. The peer mentoring program was a freshman intervention at a public historically black four-year institution, located in Tennessee. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]