In a recent paper, Reardon found that the relationship between family income and children's academic achievement grew substantially stronger in the 1980s and 1990s in the United States. We provide an international context for these results by examining the income-achievement association in 19 other Organisation for Economic Co-operation and Development countries using data from the Progress in International Reading Literacy Study and the Programme for International Student Assessment. First, we calculate and compare the magnitude of "income achievement gaps" across this sample of countries. Second, we investigate the association between the size of a country's income achievement gap, its income inequality, and a variety of other country characteristics. We find considerable variation across countries in income achievement gaps. Moreover, the U.S. income achievement gap is quite large in comparison to this sample of countries. Our multivariate analyses show that the income achievement gap is positively associated with educational differentiation, modestly negatively associated with curricular standardization, and positively associated with national levels of poverty and inequality.