Junior's first week at Reardan is disorienting for several reasons, but they all stem from his insecurity at journeying into a completely new territory, where he is basically a foreigner. Add to this the fact that he doesn't have very much support from the reservation for deciding to go to Reardan. Several key details and events factor into Junior's disorientation.
First, he is the only non-white kid at the entire school. The glaring physical differences between him and the others are the first thing he notices. "Those kids weren't just white. They were translucent" (56). It is an added blow to his confidence that the only other Indian in the school is the school mascot.
When he enters his first class on the first day of school, his presence causes everyone (including the teacher) to stop and stare. When Penelope, a beautiful girl in front of him turns and speaks to him, kindly at first, Junior is thrown off guard. She is laughing at him in the very next moment, however, along with other girls nearby. He is disoriented because he is immediately attracted to this girl, who seemed interested at first but then makes fun of him. And only a short time after this, Penelope really does take a genuine interest in Junior, which adds to his social disorientation. It is like he cannot figure anyone out.
In addition to his physical differences from the kids at Reardan, Junior is disoriented by social differences. On the reservation, he grew up knowing and understanding social rules. One of the most important things he knows as an Indian kid is how and when to fight. In some ways, Junior probably expects to be bullied at his new school. However, when an older Reardan boy picks on him at school, Junior reacts under the rules of the reservation and punches him. It is very disorienting, therefore, when the older boy does not fight back, and then ends up respecting him as a result of Junior's cultural response to being picked on.
He got to his feet and walked away. His gang stared at me like I was a serial killer, and then they followed their leader.
I was absolutely confused (65).
Finally, it is important to understand that Junior has been a social outcast his entire life. He is used to being picked on. He is used to having no friends. He expects to go to Reardan and experience the same thing, but possibly to a more intense degree, given the odds he assumes are stacked against him. So in addition to the most obvious ways Junior is physically and socially disoriented, he is also thrown off when the kids are Reardan eventually accept him and begin to like him. It is an altogether new experience and one that Junior isn't wholly ready to trust. He believes he doesn't deserve it.
Reardan was the opposite of the rez...I didn't deserve to be there. I knew it; all of those kids knew it. Indians don't deserve shit (56).