School segregation in the United States is the separation of students based on their race. This has taken two forms, legally mandated segregation (historically), and segregation in fact. In the United States, public schools are primarily a U.S. state and local matter, not a national matter, and historically, public school systems in parts of the United States were racially segregated by law (see, Jim Crow laws). All such laws were overturned in the 1950s and 1960s, but for a variety of reasons racial concentrations continue in many areas. Currently more than half of all students in the United States attend school districts with high racial concentrations (over 75% either white or nonwhite students) and about 40% of black students attend schools where 90%-100% of students are non-white. Con