Prior research indicates that individuals are more likely to take political action (e.g., vote, contact representatives, protest) when they have higher levels of "political efficacy," the belief that one's actions can influence political processes. In this mixed methods longitudinal study, I draw on Wenger's and Bandura's theories of social learning to examine how adolescents' political efficacy developed during their experiences in a Model United Nations club. Through analyses of data from questionnaires, interviews, and observations, I found that students' political efficacy increased as they became active club participants. Supportive relationships with club peers and advisors encouraged regular involvement, which in turn provided participants repeated opportunities to prepare for and practice authentic political tasks--experiences that supported their political efficacy. These findings enhance our understanding of successful democratic education and have useful implications for educators and researchers interested in political engagement.