The sixteen narrators: Amy (Wavy's cousin), Grandma, Wavy, Lisa DeGrassi (Wavy's 3rd grade teacher), Kellen, Dee (one of Liam's girlfriends), Butch (works for Liam?), Donal, Patty (home nurse), Miss Humphries (store owner/worker), Cutcheon (Kellen's employer), Casey (another home nurse), Sheriff Grant, Court Reporter, Renee (college roommate), Judge C.J. Maber
Each one contributed something vital. I questioned the importance of Butch until I went back and re-read his first 'words'. I can tell you why Wavy doesn't talk. That's what happens when you mom grabs you by the hair, and gives you a good shake while screaming in your face, "Don't you ever talk to people! You don't talk to anyone". (page 147)
Notice that Val, Liam and Aunt Brenda never say a word. Even though they are very important characters! That is an excellent way to get the reader to not know them and, as a result, have no empathy or sympathy.