Put away those dictionaries, Shmoopers: this one is an easy read. Okay, every once in a while you're going to run across a word like "contentious" (12.52), but this is a book narrated by a someone remembering herself as a six-year-old. Even smart six-year-olds are still a little, well, dumb. Most often, we get language like this: "Baby, it's never an insult to be called what somebody thinks is a bad name. It just shows you how poor that person is, it doesn't hurt you" (11.109).
Important moral lesson? Sure, absolutely. But Lee isn't trying to make you work for it.