Substantial uncertainty exists about the impact of school quality on the black-white achievement gap. Our results, based on both Texas Schools Project (TSP) administrative data and the Early Childhood Longitudinal Survey (ECLS), differ noticeably from other recent analyses of the black-white achievement gap by providing strong evidence that schools have a substantial effect on the differential. The majority of the expansion of the achievement gap with age occurs between rather than within schools, and specific school and peer factors exert a significant effect on the growth in the achievement gap. Unequal distributions of inexperienced teachers and of racial concentrations in schools can explain all of the increased achievement gap between grades 3 and 8. Moreover, non-random sample attrition for school changers and much higher rates of special education classification and grade retention for blacks appears to lead to a significant understatement of the increase in the achievement gap with age within the ECLS and other data sets. (Contains 20 tables, 2 figures and 42 footnotes.) An appendix is included which develops the decomposition presented in equation (1). [Support for this work has been provided by the Packard Humanities Institute.]