In this qualitative study, we explored the experiences of 26 engineering student mentors and mentees in a peer mentoring program. We found that mentors and mentees exploited the mentoring program's fluid structure and situated social relationships to enact a specific type of academic/professional goal and identity conducive to their entry to one of two communities of practice, the on-campus engineering program community and the community of professional engineers. The mentoring program functioned as a social space in which identities of these students converged and diverged, creating a subtle tension and self-reflection in relation to the two different communities of practice that they pursued.