Municipalities throughout the U.S. enforced racial segregation in the schools since the founding of public education systems. Their constitutional right to do so was upheld by the U.S. Supreme Court in Plessy v. Ferguson, 163 U.S. 537 (1896). However, in the landmark case, Brown v. Board of Education, 347 U.S. 483 (1954), the Supreme Court overruled Plessy and forbad state and local governments from practicing racial segregation. Despite this legal change, some public schools today are more racially segregated today than when Brown was decided in 1954. School segregation even increased in the 1990s. (Jeffrey Rosen, "The Lost Promise of School Integration", New York Times, April 2, 2000, A1, 5.) As this 2000 map of school segregation illustrates, black/white segregation is highest in counties with high black populations. (Compare with the 1980 census map of the distribution of blacks in the Eastern/Central U.S.)
Why has the law failed to undo the segregation that was originally caused by the law? The most obvious reason is that racial segregation of neighborhoods remains the norm in the U.S., as demonstrated in the city maps on this site. To the extent students attend neighborhood schools, they are likely to have few classmates of other races. But the courts, too, have played a role--initially by acquiescing in state resistance to desegregation, more recently by attacking the tools states use to achieve integration.