How about: This is "art" and we wouldn't want to interfere with the teacher's freedom of expression. Why, the ACLU will probably argue that this teacher's sick hobby should be funded by taxpayers and displayed in a museum.
That’s about as good as any I suppose. What do you want to bet this guy has a record somewhere else? If my kids were in that school their arses would be yanked out the moment I heard of this until the guy was banned from coming within 1000 yards of it.