You'd probably need two hands and two feet and a tail to count all the books you've read in which the young protagonist comes of age by the end of the book: The Outsiders. To Kill a Mockingbird. The Perks of Being a Wallflower. Pretty much everything by Gary Paulsen. So you know the drill by this point.
But in Nation, the book starts with Mau having already completed his coming-of-age ritual. All done! So now he's a man and we can move on... right? Right? Well, Nation shows that it's not that easy. You can't just flick a switch and suddenly become an adult. (We wish. Maybe if that happened, we'd stop running out of laundry detergent at 11 p.m. the day before a big job interview.) It's an ongoing process of learning to take control of your life and make your own decisions.