Higher education must improve student retention and graduation rates to meet increased demand for STEM degrees in the workforce projected for the next ten years. The high rate of attrition among STEM students entering college compels institutions to implement strategies that improve student retention because more states now employ performance-based funding models with increased pressures to improve student outcomes, such as first- and second-year retention rates. We piloted a two-year hierarchical mentoring model as part of a first-year experience course developed for biology students (BioSkills) to increase retention rates among first-time-in-college (FTIC) students. We describe the mentoring structure we adopted and how the design of BioSkills supports and educates future biology professionals. Our findings show that FTIC students who participated in this program earned significantly higher first-year GPAs and were retained at higher rates than students who did not participate, which documents the impact of BioSkills as a successful first-year intervention. However, we were surprised that the benefit of BioSkills was not replicated among under-represented minority (URM) students. We briefly speculate on explanations for this finding. Lastly, we offer best practice suggestions for future implementation.