This study examines how family and school social capital moderate the relation between family income and academic achievement. I use the data from the Korean Educational and Employment Panel(KEEP) on the third year middle school students in 2004. Results show that higher levels of family and school social capital, as well as financial capital such as family income are more positively associated with academic achievement. In addition, family and school social capital are served as moderators of the influences of family income on academic achievement. For example, higher parental concern about children and teacher-student bonding provides an extra boost to the positive relationship between family income and student achievement. Furthermore, lower educational expectations can make the relation between income and achievement negative. These findings underscore the importance of social capital at home and at school as the alternatives to promote academic achievement. In particular, greater concern and support encouraging social capital at home and school should be directed at low-income students who are struggling with academic achievement.