Purpose: The purposes of this study were to describe the roles mentors enacted as part of an afterschool science, technology, engineering and mathematics (STEM) program and how those roles varied across three sites and to explain those differences. Design/methodology/approach: The authors used a comparative case study design and collected data primarily from interviews with program mentors and observations of the sessions. Findings: The authors found that the mentors played four roles, depending on the school site: teachers, friends, support and role models. Mentors interpreted cues from the environment in light of their own identities, which ultimately led them to construct a plausible understanding of their roles as mentors. Research limitations/implications: The authors identify four mentoring roles that are somewhat consistent with prior research and demonstrate that the roles mentors enact can vary systematically across sites, and these variations can be explained by sensemaking. This study also contributes to research on mentoring roles by elaborating each identified role and offering a framework to explain variability in mentor role enactment. Practical implications: The authors recommend that mentoring program directors discuss the roles that mentors may enact with mentors as part of their training and that they engage mentors in identity work and also recommend that program managers create unstructured time for mentors to socialize outside STEM activities with their mentees. Originality/value: This study contributes to mentoring research by using sensemaking theory to highlight how and why mentoring roles differ across school sites.