This paper presents tests and estimates of the human capital model of income inequality using synthetic cohort data for Thailand: 19922011. The model focuses on four primary determinants of income inequality: mean per capita income levels, the variances in years of education, in the number of children, and in the number of earners in the household. All of these factors areimportant sources of income inequality in Thailand, with relative impacts that differ across demographic groups and types of household structure. An invertedU relation between mean per capita income levels and inequality is found, reflecting gender differences of the head of household, differences in household composition, and variation in access to finance. Although the human capital model emphasizes education, estimates presented here show other household characteristics, such as numberof children and number of earners, can be even more important sources of inequality.