I'd suggest finding out what topics all classes are studying or are going to study and get a range of books on those topics. I'm in Y2 on a morning and can the kids all look for books on the topic we are studying. Even reluctant readers! The boys in the class nearly always go for nonfiction rather than fiction books. Last term there were no books left in the library that had anything to do with space or planets - they were all in our classroom, lol.