I guess it's because the black kids behave worse. Before anyone gets mad I am black and five members of my family are teachers. Each one of them says that the kids who give them the most trouble are black boys.
If you take a kid, create conditions where there is no father and not much of a mother, "raise" him in a part of town where everything is ugly, mean and crooked and tell him that learning or just shutting up and sitting down is behaving like a hated white kid then don't be surprised if he becomes the problem child in class.
One of the dumbest things black women ever did was to listen to the feminists and the hippies in the 60s. The message of free love, scorning marital convention and encouragement of underclass women to have babies with the expectation the government would take care of them forever was not a good thing. It ruined the black family.
The hippies grew up or moved on to other causes. They're still liberals but they live in the burbs and send their kids to private school. The feminists still hate men in public but many either give it up when they finally meet a man or keep their love lives private. When Gloria Steinem got engaged to a very rich old man a number of feminists were furious but she got married anyway. For black women the way back isn't so easy (the pool of marriagiable black men is not that big and these men usually don't want a woman who already has somebody else's kids) and the kids are a reflection of that.
In the forty's and early fifties, black enclaves had married men, stable families, church going people. Stable enclaves, with very low crime. Proud families, working hard, rising up.
Then came the liberal BS. Ruined the close knit communities.
Sing Out, Sister! You are so right, sooooo right. Soooooooo right....