If you have a kid in such a school who is introducing kids to movies and non Jewish music that can also be grounds to throw him out. Now like I said it depends on the school and the homes that the kids come from and what type of Hashkafos the school is geared towards.
So you are allowed to be a Rotzach to keep a chumra/point of Hashkafa.
I know you don’t see it that way, but the scores of OTD children who have been told they are not “good enough” tell another story.