A web-based survey of members of the Society for the Advancement of Chicanos and Native Americans in Science tested a model that proposed that the effects of science support experiences on commitment to science careers would be mediated by science self-efficacy and identity as a scientist. A sample of 327 undergraduates and 338 graduate students and postdoctoral fellows described their science support experiences (research experience, mentoring, and community involvement); psychological variables (science self-efficacy, leadership/teamwork self-efficacy, and identity as a scientist); and commitment to pursue a career in scientific research. Structural equation model analyses supported our predictions. Among the undergraduates, science (but not leadership/teamwork), self-efficacy, and identity as a scientist fully mediated the effects of science support experiences and were strong predictors of commitment. Results for the graduate/postdoctoral sample revealed a very similar pattern of results, with the added finding that all three psychological mediators, including leadership/teamwork self-efficacy, predicted commitment.