Recently, I started ordering books from the library after researching various book lists (Honey From a Child's Heart and the books used in Five in a Row). I've noticed some amazing differences in the quality of literature from reputable lists versus what my children randomly pick up at the library. It's not always a good thing to be able to pick from thousands of books when such a large percentage of them have terrible themes, iffy artwork, and in general promote ideals that I don't agree with.
If I ever felt bad that my child was "missing out" on the school experience, I am forever cured after listening to a Dan Gutman book on tape. Now my son can spout off such excellent quotes as "So's your face" and learned fabulous lessons like "girls like school and boys don't" and "I don't want anything boring for Christmas like clothes or food". A whole year's worth of lessons on humility, kindness, and a love for reading down the drain from one random stop at the library before a road trip. There was a limited selection, but I definitely should have gone with Misty of Chincoteague over the "Weird School" series. Even if Misty would have been a little above his level, at least it wouldn't have caused the same problems.
Lesson learned: if you don't review your child's literature before, during, or after they read it, you will miss out on a lot of fabulous lessons they may (or may not) be learning. Quality literature is more than just the library's recommendation, or purchase. The most popular author may not be the most educational, and your child's choice may end up teaching him or her something you never intended. Grade/age level is not always the best guide to choose your literature.