The parents should be more than infuriated. They should sue the school district big time.
Yup, I have to imagine that this violates all sorts of local policies, and probably local and state civil laws as well. Maybe even some criminal ones. And I think a whole load of Federal Civil Rights statutes are in play as well.
On the Constitutional side theres definitely a First Amendment violation. If disparate treatment in both policy and enforcement can be shown, there’s a 14th one as well.
So time to find a patron that will financially support suing the school and those involved to the extent permitted by the law. Including filing criminal charges (if applicable). Make the school and the bullies wage an expensive and time consuming legal defense, see if they’re willing to go under oath trying to justify their actions.