In the U.S., some schools have removed books for various reasons. Sometimes it's racial stereotyping like with Huckleberry Finn. Sometimes it's the complaint that the material is too intense like Anne Frank's diary or "The Giver." Other times it's because a gay relationship is depicted in a positive way and some people find that offensive or think it will turn their kid gay if they read it.

I think high schools (14-18 year olds) should have a great deal of leeway in the books the school library carries. The situation with younger children is more problematic. You can't remove every book that mentions God, for instance. (Well, you could but it would seriously limit the number of books in the library.)

Parents absolutely should be notified of assigned reading and given an opportunity to weigh in. If they object to the book, the student should be allowed an alternative assignment.

Children's books tend to teach values and not everyone shares the same ones. It's a tough situation.