It's not a race issue so much as a poverty and cultural issue. Any racial correlation is a proxy for those two things.
There just aren't enough blacks in the US for them to completely dominate any crime. To be at your imagined rate of 90% of instances being black, when only 13 or 14% of the population, would require a ridiculously high rate compared to every other group.
https://www.edweek.org/policy-politics/education-department-...
Let's take aside the charged component of this and just suppose hypothetically that 100% of the assaulting students belonged to some subgroup. So what?
They may be 100% black, or 100% male, or something, but it's not like you can reasonably just say "So no males at our school." Regardless of whether you can find a subgroup who this belongs to with a very low specificity, you still need policies that tackle the behavior itself rather than trying to find some really weak predictor.
Yeah, no.