What does it mean for Arnold to be a "part-time Indian?"
In Sherman Alexie's book, The Absolutely True Diary of a Part-Time Indian, Arnold Spirit Jr. (nicknamed "Junior") leaves the school of his reservation to go to a "white" school a few towns away. Arnold has a bit of an identity crisis, because he no longer feels fully "Indian," but he doesn't feel white, either. Arnold has always been outcast and picked on because of his physical abnormalities, and this only adds to the Othering he feels both on and off the "Rez." He splits his time between the Spokane Reservation, where his family live, and the white high school where he seeks opportunity.
Arnold decided to go to the white school, even though it's far away, because he was fed up with the lack of opportunity and resources people on his reservation must deal with. The schoolbooks are outdated, the Indian Health Services aren't helpful, and there aren't any jobs. Arnold is angry that his family is poor and stuck in a cycle of poverty. He wants to do better for himself and his family, and even though going to a white school makes him feel like he is denying some part of his heritage, he knows it is the only chance he has.
Arnold is a brave character who sacrifices some of his identity in order to have better opportunities in life. Such a struggle doesn't only happen in books. In fact, author Sherman Alexie made the very same choice to go to school off of the reservation he grew up on. Many First Nations people have been forced (explicitly or implicitly) to express their identities on a part-time basis in favor of becoming more "white" and attaining a better lifestyle. Racism like this has become endemic in the culture of the United States, and the Part-Time Diary offers important insight into what it is like to live such a life.