Using data from the Korean Educational Longitudinal Study of 2005-2007, the current study investigated the role of family and school social capital in students' academic achievement in South Korea. Results showed that while some forms of family and school social capital were associated with increased math achievement, the effect of family social capital was greater than that of school social capital. Results also suggested that similar to parents who play a key role in shaping social capital at home, teachers may play an important role in building ecological school social capital such as collective school norms, which was found to affect students' academic achievement. In addition, results found some interaction effects between family social capital and school social capital. Specifically, collective school norms were found to compensate the deficiency of parental involvement in school, while student-teacher relationships and academic emphasis had boosting effects with parental educational expectation on students' academic achievement. Features of Korean education related to the distinctive role of family and school social capital in students' academic achievement and policy implications were discussed.