Drawing on first-third wave data from Seoul Educational Longitudinal Study(SELS), this study
attempts to examine the effect of school population socioeconomic composition on individual
academic achievement focusing on the moderating effect of individual socioeconomic status(SES).
Our hierarchical linear modeling(HLM) results show that the heterogeneity of socioeconomic
composition, which is measured by standard deviation of SES of school population, does not wield
a statistically significant influence on individual academic achievement. However, school mean SES
noticeably exerts a significant impact on individual academic achievement. In addition, cross-level
interaction effect between individual SES and school mean SES, which is taken into account to
analyze how the school composition effect varies by individual SES, suggests that students with
higher SES benefit more from a higher school mean SES than students with lower SES, thereby
widening the gap of academic achievement between the upper and the lower class in schools with
higher SES. Based on the findings, policy implications are briefly discussed.