What makes a teaching read?

Some books include facts so naturally you wonder afterward where you learned these things. Experiencing life like a different character, we learn, perhaps, where snow falls deepest or how to soothe the savage beast. But other books offer their lessons more directly, like children's picture books with a moral to tell. Of course, if the book happens to be a children's picture book, the lesson's expected. But how much information is too much information in a novel? Or, at the other end of the sc...