I don't know. I doubt racism is the topical cause. Blacks are probably suspended disproportionately because they misbehave disproportionately. Getting at the root cause could likely uncover racism, and probably already has, as one of the main reasons blacks are at a disadvantage in American society, on average. If that's the case, then it's probable that a black student would be more likely than a white student to show up at school, under-rested, under-nourished, under-dressed, un-loved, and otherwise unprepared to learn. Hence, they misbehave and are more likely to be suspended.

I've had a lot of friends and relatives in education, and I was initially surprised to learn how prevalent social dysfunction is, cutting across racial and economic classes. However, as expected, blacks and hispanics are hit disproportionately harder.