Background: School-based social-emotional and character development (SECD) programs can influence not only SECD but also academic-related outcomes. This study evaluated the impact of one SECD program, Positive Action (PA), on educational outcomes among low-income, urban youth. Methods: The longitudinal study used a matched-pair, cluster-randomized controlled design. Student-reported disaffection with learning and academic grades, and teacher ratings of academic ability and motivation were assessed for a cohort followed from grades 3 to 8. Aggregate school records were used to assess standardized test performance (for entire school, cohort, and demographic subgroups) and absenteeism (entire school). Multilevel growth-curve analyses tested program effects. Results: PA significantly improved growth in academic motivation and mitigated disaffection with learning. There was a positive impact of PA on absenteeism and marginally significant impact on math performance of all students. There were favorable program effects on reading for African American boys and cohort students transitioning between grades 7 and 8, and on math for girls and low-income students. Conclusions: A school-based SECD program was found to influence academic outcomes among students living in low-income, urban communities. Future research should examine mechanisms by which changes in SECD influence changes in academic outcomes.