I will respectfully disagree for my school. My school covers grades four through eight, a very unusual grade configuration. The 8th grade has books in the Holocaust collection that are graphic and extremely intense: I do not let 4th graders check them out. Many 8th graders read The Book Thief. Shall I check that out to 4th graders? Speak? Wintergirls? Inventing Elliot? The Chocolate War? There are too many examples to list.
There are books that are perfectly appropriate for 13 or 14 year old students that are not appropriate for 8 or 9 year old students. If a parent argues to the principal that his/her child should be allowed to take out a book, he will discuss it with the parent and make the decision.
Wondering about the Wimpy Kid books is one thing; the books above are quite another.