This article has two basic objectives: First, to examine whether educational expansion in south Korea has contributed to the abolishment of class differentials in educational attainment. Second, to examine what has deterred greater equality of educational attainment in a South Korean context. A wide range of research on education in South Korea has focused on the primary effects - relationship between socioeconomic background and students’ academic achievements in school – in creating class differentials in the pursuit of higher education. This paper further investigates the secondary effects of pursuing tertiary education – the actual choices that students and their parents make in regard to educational options on the basis of their socioeconomic background when holding the academic achievement constant. Using Korean Educational Longitudinal Survey (KELS 2005), this research demonstrates that educational expansion does not necessarily correspond to greater equality of educational opportunity regardless of social origin in South Korea. This empirical examination indicates that educational mechanism still reproduces the class differentials in educational attainment through both primary and secondary effects. Students from privileged background tend to perform better in schools and thus, they are more likely to pursue tertiary education than their peers from disadvantaged background. However, even when the demonstrated academic abilities are the same, students make different choices in pursuing higher education based on their socioeconomic background and gender. This research shows that in South Korea, socioeconomic background appears to work in different way as in the European context.