Call attention to as many of your child's classmates as you can and tell them this is a filthy, disgusting book, and they should NOT read or study it, and condemn the teacher(s) pushing it, tell your child and their classmates that that teacher is a very bad person, and out to be ashamed of himself/herself.

IOW, treat it the very same way if a teacher showed a class some XXX filthy porn and instructed them to study it. Go ballistic of you have to. Don't worry about the principal for now. Go to all the kids first.