Explanations for U.S. students' performance on international comparisons of educational achievement abound, with much of the scholarly and public discussion centering on cross-national differences in education systems. The author argues that the connection between economic inequality and educational achievement in affluent societies deserves far more attention than it receives. Analyses of data from the 2006 Programme for International Student Assessment and other sources indicate that egalitarian countries have higher average achievement, higher percentages of very highly skilled students, and lower percentages of very low-skilled students than do less egalitarian countries. These patterns suggest that egalitarianism and educational excellence are compatible goals for affluent societies. The author discusses the implications of these findings for educational and economic policy in the United States. (Contains 2 notes, 2 tables, and 3 figures.)