These cards can be printed and placed on the outside of baskets in your classroom library. They correlate with the Accelerated Reader program. My school has students check out books according to their reading ability (i.e. A student reading on a first grade level would check out 1.0-1.9.). I have set up my classroom library the same way so it is easier for students to check out books that are a good fit for him or her. They can easily place them in their designated baskets, as well. This prevents a messy, unorganized classroom library.
FYI- Accelerated Reader levels can be found on Scholastic's Book Wizard. You type in the book title and it gives you the AR level and the lexile level.