What are some themes in The Absolutely True Diary of a Part-Time Indian?

I think in addressing this question, the most powerful theme that is evident is the reclamation of voice.  A central idea of this book is the notion that a person's voice can be authentic and claimed back despite social marginalization and political powers that seek to silence it.  Ask yourself about occasions in the book where we can see Arnold fight to reclaim his voice.  Another theme is the idea that a person's identity is forged through social and political hurdles.  Arnold's identity and notion of self is enhanced only when he undergoes extreme levels of challenge from his own people and white society. (Pay attention to his impressions about how he feels he fits in, or more appropriately, does not fit in within either society.)  Like most books that are bildungsroman novels centered on the notion of a marginalized group, this novel explains the difficulty in being considered a hyphenated American.  I think this is another theme that can be explored with examples from the text.  The final theme is something that I find intriguing, but I am not sure others would.  I would submit that a theme present in the book is how these voices can be brought from margin to center when we pay attention and listen to these voices.  The narratives of Native Americans have not been included in American history.  Pay attention to the evidence in the book that talks about how Arnold sees himself as an American whose voice "sings" America, even if American society itself does not fully acknowledge his voice.  He speaks and sings regardless of who listens.  This idea of the freedom within the American narrative is a powerful one.