Thirty states passed laws forbidding and sixteen still had them in 1968 when the u. s. supreme court finally ruled that they violated "the equal protection of the laws" guaranteed by the fourteenth amendment.

The answer is interracial schools. School segregation in the US started in its de jure form with the passage of Jim Crow laws in the late 19th century. It is affected by the history of southern states as  patterns of residential segregation, slave societies, and later school selection programs, and Supreme Court rulings about past school desegregation efforts.