WASHINGTON (AP) — Seventy years ago this week, the U.S. Supreme Court ruled separating children in schools by race was unconstitutional. On paper, that decision — the fabled Brown v. Board of Education, taught in most every American classroom — still stands.

But for decades, American schools have been re-segregating. The country is more diverse than it ever has been, with students more exposed to classmates from different backgrounds. Still, around 4 out of 10 Black and Hispanic students attend schools where almost every one of their classmates is another student of color.

The intense segregation by race is linked to socioeconomic conditions: Schools where students of color compose more than 90% of the student body are five times more likely to be located in low-income areas. That in turn has resounding academic consequences: Students who attend high-poverty schools, regardless of their family’s finances, have worse educational outcomes.