I suspect there is a correlation between the race of the teacher and the race of the students. I’m not sure exactly why (perhaps they tend to live in the same neighborhoods, or voters tend to elect local school officials of their own race, and these officials hire more people of their own race).
It’s very possible that the real issue is that they are hiring (and retaining) sub-par minority teachers, and just happen to be inflicting them on the minority students.
That is the unspoken assumption in the lawsuit, and it is probably correct.