A big discussion has been going on for a few days at one of my listservs about the proposal in the U.K. to start banding books with age levels. I brought age banding up to a family member who's an education major doing her student teaching this fall in a fifth grade classroom. She told me about children determining the appropriateness of books for themselves using the Five Finger Test.
Basically, children read a page of a book and hold up a finger everytime they hit a word they don't know. If they have five fingers up by the time they reach the end of the page, they can assume the book is too difficult for them just then and try something else. The idea is to keep child readers from becoming frustrated and, potentially, turned off from reading altogether.
I think the Five Finger Test could work for me, too. Certainly if there are five words on a page that I don't know, the book is no doubt too frustrating for me. The difference between child readers and myself is that child readers have the hope that at some time in the future their reading level will be high enough that they can go back to the book they found too difficult and read it successfully. I'm not so sure that's going to happen for me.