Research suggests that participation in co-curricular and extracurricular activities improves students' academic outcomes, but less is known about the mechanisms by which these programs impact students' educational trajectories. This study examines psychosocial factors linking participation in an urban debate league (UDL) and academic performance in a large prospective study of students in the Chicago Public Schools (N = 12,197) over a nine-year period. School, social, and civic engagement were higher among debaters than non-debaters, but mediation analysis indicated these indicators of engagement only partially explained the academic effects of UDL participation. This article discusses study implications for co-curricular programming, in particular as they relate to efforts to close racial/ethnic and socioeconomic disparities in educational attainment.