Law professor Eugene Volokh quotes Defoe v. Spiva on a "First Amendment Exception" for speech about race, where a two-judge majority wrote:
"A public high school that can put reasonable limits on drug-related speech by students [referring to Morse v. Frederick, which upheld such restrictions —EV] can put reasonable and even-handed limits on racially hostile or contemptuous speech, without having to show that such speech will result in disturbances. Expressions of racial hostility can be controlled in the public schools even if students in the attacked racial group happen to be mature, goodnatured, and slow to react."
Those would be the white kids, I suppose. And they'd have to accept"expressions of racial hostility" because they're in their textbooks.
More seriously, the Sixth Circuit really has found a racial hostility exception, and declined to rehear it. First Amendment expert Volokh doesn't approve—see The Volokh Conspiracy First Amendment Exception for ”Racially Hostile or Contemptuous Speech,” Including Display of the Confederate Flag, in K-12 Public Schools – Denial of En Banc Rehearing by Sixth Circuit.