Few studies have empirically investigated the specific factors in mentoring relationships between undergraduate researchers (mentees) and their mentors in the biological and life sciences that account for mentees' positive academic and career outcomes. Using archival evaluation data from more than 400 mentees gathered over a multi-year period (2005-2011) from several undergraduate biology research programs at a large, Midwestern research university, we validated existing evaluation measures of the mentored research experience and the mentor-mentee relationship. We used a subset of data from mentees (77% underrepresented racial/ethnic minorities) to test a hypothesized social cognitive career theory model of associations between mentees' academic outcomes and perceptions of their research mentoring relationships. Results from path analysis indicate that perceived mentor effectiveness indirectly predicted post-baccalaureate outcomes via research self-efficacy beliefs. Findings are discussed with implications for developing new and refining existing tools to measure this impact, programmatic interventions to increase the success of culturally diverse research mentees and future directions for research.