By definition, whatever is taught in a public school is government-mandated speech. Hence, the concept of “freedom of speech” is not applicable to the public school curriculum.
I find it quite unbelievable that people don’t get this. The constitutionally guaranteed freedom of speech prohibits the government from punishing individuals for saying things that the government doesn’t like. It doesn’t protect the government from having to hear things it doesn’t like.
Governments don’t have freedom of speech. The concept is ludicrous. Who would they be free from?