De facto segregation is a natural type of segregation that is not the result of a legal requirement. It happens through gentrification and, consequently, there are demographic areas in the United States that are predominantly of the same ethnicity. By default, the school system in those areas will have demographics that are predominantly the same—such that schools in some areas will consist of over 90% of the same ethnicity.
De facto segregation was referenced often in the Civil Rights Movement of the 1960s and 1970s, where communities accused the federal government of allowing this type of segregation to continue overtly. In turn, the federal government put statutes in place that gave all U.S. public schools the right to financial help (up to a certain point).