This study has analyzed the effects of educational reforms on social class differentials in school transitions over time in Japan and Korea. Previous research has found that social class differentials have not decreased over time despite a rapid expansion of education, and that the reforms have not led to a reduction in educational inequalities. However, in case studies about states where education is strongly controlled or closely regulated by government authority, some authors have insisted that strong states may increase or decrease the effect of class on education. In this analysis, we analyzed whether or not the change from the old educational system to a new one (single ladder system) affected social class differentials during a ten-year period in Korea and Japan. As a result, we found that only Japan’s case shows significant results for reducing the gaps between social classes due to the change of educational policies. Although Korea has experienced fast expansion of education since the introduction of single ladder system at the same time as Japan, the Korean government could not provide substantial funding for education due to a lack of public expenditures and the Korean War, while the Japanese government realized this during the 1950s. If the state does not play a leading role in the realization of educational reforms, we cannot expect that its reforms will have substantial effects on associations between one’s social class and one’s continuation of one’s education. Furthermore, although the promotion policies on educational opportunity may reduce gaps between social classes, this does not automatically reduce inequality in educational opportunity.