On average, black students typically score one standard deviation below white students on standardized tests--roughly the difference in performance between the average 4th grader and the average 8th grader. Historically, what has come to be known as the black-white test-score gap has emerged before children enter kindergarten and has tended to widen over time. Gaining a better understanding of what causes the test-score gap is of great importance because eliminating the gap could yield great advances in the well-being of African-Americans. To take a fresh look at the gap and its sources, the authors examined a new data set, the Early Childhood Longitudinal Study Kindergarten Cohort, compiled by the U.S. Department of Education. The results are quite surprising: after adjusting the data for the effects of only a few observable characteristics, the black-white test-score gap in math and reading for students entering kindergarten essentially disappeared. Put simply, white and black children with similar personal and family background characteristics achieved similar test scores. Once students enter school, however, the gap between white and black children grows, even after controlling for observable influences. The authors speculate that blacks are losing ground relative to whites because they attend lower-quality schools that are less well maintained and managed as indicated by signs of social discord. Though they recognize that they have not provided definitive proof, this is the only hypothesis that receives any empirical support. (Contains 2 figures.)