This study investigated the role of peer mentoring and voluntary self-development activities (i.e., capitalization) in anchoring science, technology, engineering, and mathematics students to their college majors. Online data were collected from 214 undergraduate students. As hypothesized, mentoring was positively related to capitalization, and both mentoring and capitalization were positively related to satisfaction with one's major, affective commitment to one's major, involvement in one's major, and willingness to be a mentor. Contrary to expectations, capitalization did not mediate the relationship between peer mentoring and student outcomes, suggesting that these constructs contribute independently to positive outcomes. Implications and future research directions are discussed. (Contains 1 table.)