what does it mean for arnold to be a part-time indian?

Arnold sees himself as a "part-time Indian" after he transfers to a "white" school. He feels as if he's two different people depending upon where is and who he's with. Thus, both identities are somewhat similar and seen as part-time. When he's home on the reservations, he's Junior..... when he's at school, he becomes Arnold. Junior and Arnold, of course, are the same person conforming to the expectations of two different cultures.