Note: This post covers American schools, but not universities, from 1954 to 2007:
In the early 1900s most blacks in America were required by law to go to separate schools than whites. These schools got way less money than white schools. Schoolbooks were between old and missing. Many teachers did not even have university degrees.
In 1954 the Supreme Court in Brown v Board said blacks had the right to go to white schools.
In 1965 the president signed Executive Order 11246. It said the government would cut off money to any school that did not make a good faith effort to allow blacks and whites an equal chance to attend. In 1968, 78% of blacks in the South went to schools that were less than 10% white. In 1972 only 25% did.
Busing: A common way to desegregate schools was through busing: by making students take a bus to school, the school district could send students to different parts of the district to achieve a good mix of races.
Also in 1965 the president signed the Voting Rights Act, which outlawed any practice that kept blacks and other people of colour from voting.
In 1969 Richard Nixon became president. He won by using the Southern Strategy, by appealing to white racist voters, particularly those in the South. As part of that strategy he appointed judges to the Supreme Court who were against desegregation in schooling and housing.
By 1974 four of the nine judges on the Supreme Court had been appointed by Nixon. That was enough for the Court, in Miliken v Bradley, to limit school desegregation to school districts only, not to metropolitan areas.
White flight: Miliken v Bradley meant middle-class whites could escape school desegregation by white flight, by moving to white school districts. So while many cities and Southern counties desegregated their schools by race, most schools in white suburbia remained nearly all white.
In the 1990s the Supreme Court, in Board v Dowell and other rulings, pulled back from busing. It now no longer required anyone to be sent out of their neighbourhood to another school for reasons of race. That means that school segregation, in the long term, will follow housing segregation.
Housing segregation: Most blacks, whites and Latinos in America live in racial ghettoes: neighbourhoods where most people belong to their own race. While housing segregation by race is not as bad as it used to be, in part because restrictive covenants and blockbusting have been outlawed, it is still at shockingly high levels. That is partly because racial steering by real estate agents which, though outlawed, is still widely practised.
In 2007 most whites went to schools that were mainly white while most blacks went to schools that were mainly black.
Tracking: Even when a school is mixed-race, classrooms often are not. Through test scores, schools can put whites in separate classes than blacks and Latinos, creating two schools under one roof.
In 1957 Dorothy Counts bravely helped to desegregate the schools in her county. Since 1999 they have been resegregating.
Source: Partly based on Beverly Daniel Tatum, “Can We Talk About Race? And Other Conversations in an Era of School Resegregation” (2007).