This article reports the results of a positive youth development (PYD) intervention for adolescents in alternative high schools (209 African American and Hispanic American adolescents, aged 14-18; 118 females and 91 males). The intervention was guided by a self-transformative model of PYD (Eichas, Meca, Montgomery, & Kurtines, 2014). This model proposes that the actions youth take to define themselves function as active ingredients in positive development over the life course. Consistent with the self-transformative model, results provided support for direct or mediated intervention effects on the self-transformative processes of self-construction and self-discovery, life goal development, identity synthesis, and internalizing problems. The findings illustrate the utility of using a self-transformative approach to PYD in work with marginalized youth populations.