Coming of Age
This one is kind of a no-brainer: Maisie is six years old when we first meet her, and James follows her along a path of self-discovery and growth. We can't be sure how old she is when What Maisie Knew is over, but we do know for sure that she's wise beyond her years.
Always quick and perceptive, Maisie only gets more so as the novel progresses. And if James has his way, then we grow smarter with her—Maisie's coming of age should not only remind us of our own coming of age stories, but our reading experience should help us learn again how important moral centeredness is. Pretty much every time you learn a new, pesky life lesson, it's about as mystifying and transformational as coming of age all over again, right?
But, sheesh, without learning those moral lessons, you end up as shallow (wo)man children like Maisie's parents.