Most schools use leveled reading or guided reading to match up a child with a book at the correct reading level for them. Leveled reading uses various assessment tools to determine how well your child reads, and then matches her to books that are challenging enough for her to make progress. Books are categorized into levels of difficulty.
Among the more popular systems for reading assessment are The Lexile® Framework for Reading, Accelerated Reader (AR), Fountas and Pinnell and DRA. If you don't know your child's reading level, you can ask the teacher.
At the public library, our books are not organized by reading level, but you can find information about Accelerated Reader and Lexile levels, by using our online library catalog.