The Question and Answer section for The Absolutely True Diary of a Part-Time Indian is a great resource to ask questions, find answers, and discuss the novel.
Mr. P believes that Junior threw the book as a sign he wasn't willing to give up. All the other students on the reservation give up, but Junior was different. Mr. P was acknowledging those differences.
"But not you," Mr. P said. "You can't give...
The class is silent when Junior enters. There is a bully Roger who picks on Junior. Junior, being from the rez, is no stranger to fighting. He hits Roger, who is much bigger than him, and ironically receives respect of Roger and most students.
Junior gets suspended from school. I think, in a larger context, this helps Junior in the long run. Mr. P comes by and tells Junior that he is special and needs to get out of the reservation to make something of himself.