Background: Maybe this is a nationwide thing that doesn't need explaining, but just in case, at my DS's school they have an Accelerated Reader (AR) program, where certain books are associated with a little comprehension test the kids can take on the classroom computer to earn points. In DS's school library, the books that are in the AR program have a green sticker on the spine. So here's the talk I had with DS about it:
Me: I bet some of our books at home are AR books
DS: Maybe. We could check to see if some of them have green stickers.
Me: Well, our books wouldn't have the stickers, but we might have some of the same titles at home.
DS: But AR books are only the ones with green stickers.
Me: At school, that's true. But remember you said that the Magic Treehouse books at school have green stickers?
Me: And we have those very same Magic Treehouse books at home right?
Me: But our books don't have green stickers, but they're still AR books, right? You could read our Magic Treehouse books and still be able to take the AR test about them, right?
DS: If it doesn't have the sticker then it's not an AR book.