Our society has an extremely narrow view of what "learning" is, and where and how "learning" takes place. How much of the lessons you learned sitting in a classroom are a vital part of you, of the things you use everyday? How many of the things you learned in a non-classroom setting are a part of you?
I know quite a few people who learned to read before they started formal schooling, and then got in trouble with their teachers because they A) "weren't supposed to know how to do that yet" or B) were bored with the little sissy books they had to read, and read books that were "higher than their grade level".
I love the freedom to let my children learn to love learning. Wonderful books do not need to be classified by "grade level", "reading level" or other systems. I do feel that some books are too advanced or difficult for younger children ( from my own personal experience as an extremely precocious reader). That is one of the great benefits of reading 9and discussing together)the books your children read. The other blessing is being introduced to the amazing children's and young adult authors that are working right now.
In my opinion, there is FAR more creativity, cleverness and good writing happening in the "young adult" market than in the "adult" section. Check it out!