The Coleman report, published 12 years after the Brown decision, confirmed that widespread school segregation in the United States created inequality of educational opportunity. This study examines whether racial and socioeconomic segregation, which is on the rise in the United States, is still contributing to the achievement differences among students. The study used data from the National Education Longitudinal Survey of 1988 to estimate multilevel models of achievement growth between Grades 8 and 12 in mathematics, science, reading, and history for a sample of 14,217 students attending a representative sample of 913 U.S. high schools. The study found that the average socioeconomic level of students' schools had as much impact on their achievement growth as their own socioeconomic status, net of other background factors. Moreover, school socioeconomic status had as much impact on advantaged as on disadvantaged students, and almost as much impact on Whites as on Blacks, raising questions about the likely impact of widespread integration. The impact of socioeconomic composition was explained by four school characteristics: teacher expectations, the amount of homework that students do, the number of rigorous courses that students take, and students' feelings about safety. The results suggest that schools serving mostly lower-income students tend to be organized and operated differently than those serving more-affluent students, transcending other school-level differences such as public or private, large or small. This article then addresses the question of whether such school characteristics can be changed by policies to reform schools and funding systems versus policies to desegregate schools.