Using a sample from the Korean Education & Employment Panel(KEEP), this study attempts to highlight the current educational gap in Korea and the determinant factors causing the gap. It found that there exists a noticeable educational gap in terms of academic achievement among regions and social classes. In particular, the striking difference in academic achievement is found between the students in large cities and their counterparts in rural areas. Also, a student's academic achievement is found to be closely related to his/her father's educational attainment level, household income, and male guardian's occupational status. The remarkable disparity in academic achievement among regions is mainly due to the over-representation of highly-educated parents in large cities, coupled with the concentration of high academic achievers in large city schools through the self-selection process. The academic achievement gap observed among social classes seems to result from the tendency of educational homogamy that magnifies the effect of hereditary factors and the differences in parental interest and practical support for children's education. As such, although educational gap in Korea might be narrowed to some extent, it seems very difficult intrinsically to eliminate some causes of educational gap.