* Desegregation is a complex process: It wasn't a single event with a clear ending date. Many districts faced protracted legal battles and slow, uneven implementation of desegregation plans even after court orders. Some districts might have technically met the letter of the law, but de facto segregation persisted.
* Data limitations: Comprehensive, nationwide tracking of desegregation efforts at the district level isn't readily available.
While some districts faced significant challenges well into the 1990s and beyond, pinning down the absolute "last" is impossible due to the ongoing nature of the struggle for educational equity and the varying interpretations of what constitutes true desegregation.