This is the kind of book that comes full circle. Here's what we mean: The title of the book is The Year of Billy Miller. And the first time anyone says this phrase is when Billy's dad tells him that he's going to have a great year in second grade because "this is the year of Billy Miller" (1.1.37). By the end of the book, this phrase has become a mantra Billy says to himself. In fact, in the last sentence of the book, he makes it a special declaration:
And then, because he felt so good, and because he could not stop himself, he leaned into the silent microphone and exclaimed in a voice meant just for Mama, "This is the Year of Billy Miller." (4.5.76)
Billy has just finished his poetry show and he's on cloud nine. Not only was he able to recite his poem from memory on the second go-around, but he created a special moment for his mom as well. He's feels so great that he can hardly contain himself.
So based on these details, we know that this ending is already moving in a happy direction. And when Billy says that this is his year, he's showing us just how much he's grown since his early fears of second grade. It looks like this really was the year of Billy Miller, and that makes the ending even happier.