This study examines the impact of increased school exposure on academic achievement, particularly among disadvantaged students. In Korea, out-of-school education is provided in the public sector in order to equalize educational opportunities beyond regular schooling. Since the out-of-school education in the public sector could be considered an extension of schooling, it provides an institutional background for evaluating the compensatory role of schools. The analysis considers the likelihood that subgroups, differentiated by factors such as family structure, background, and academic achievement levels, may have different motivations and ways of using public sector out-of-school education. The results indicate that students from single-parent families spend more hours per day in public out-of-school education than students from two-parent families. There is a tendency for those from higher socio-economic families and with lower levels of academic achievements to participate for longer. Nevertheless, the positive effects of out-of-school education in the public sector on academic achievement was greater for single-parent students, as well as for students from lower socio-economic backgrounds and with lower academic achievement levels. The findings suggest that that out-of-school education in the public sector, similar to regular school programs, could improve the academic achievement of disadvantaged students.