Excellent idea....the agony of parents is nationwide so this might just catch on and put school board/bureaucrats in their place.
A lawyer or group of lawyers could set up a nice little side hustle teaching conservative parents their rights and offering those letters for a reasonable fee. They could offer a service similar to Homeschool Legal Defense Association.
Two friends at the end of last year had issues with teachers degrading white men. One’s son was forced to read the part of Juliet in a play by the teacher to open his mind. Both went in and threatened to sue after telling the principal they were offended by the teachers’ racist, and sexist behavior. Those teachers were denying their sons a safe and tolerant learning environment due to this. The other one complained about the misgendering of her son. Always use their language against them. The teachers toned it down. If more parents did that it would put the schools in notice.