We study trends in educational homogamy at six boundaries in the educational structure of 10 East-Asian societies and explain its variation using explanatory variables at the country, cohort and boundary level. Educational homogamy was higher at the higher boundaries in the educational structure. Since the 1950s it decreased at all but the lowest boundaries, indicating convergence to a relatively low level of homogamy. Educational homogamy is lower in societies that are more modern, have higher female employment and experienced less Confucian influence. Results support the general openness and the exclusivity hypothesis, which predict educational homogamy to decrease in modernizing societies and to be higher when the group of more highly educated is smaller. Findings suggest that the trend towards less educational homogamy is related to educational expansion. (Contains 5 figures and 3 tables.)