Why does Junior get so angry when he reads his mother's name in his math textbook?

In Sherman Alexie's semi-autobiographical novel, The Absolutely True Diary of a Part-Time Indian, Arnold Spirit (called Junior) becomes so fed up with life at his school that he makes the decision to go to a school miles away. Junior has grown up on the Spokane Indian Reservation, an impoverished area with little opportunity for development. Junior's friends, family, and everyone he knows are stuck in a cycle that puts them at a disadvantage. Junior's people...

In Sherman Alexie's semi-autobiographical novel, The Absolutely True Diary of a Part-Time Indian, Arnold Spirit (called Junior) becomes so fed up with life at his school that he makes the decision to go to a school miles away. Junior has grown up on the Spokane Indian Reservation, an impoverished area with little opportunity for development. Junior's friends, family, and everyone he knows are stuck in a cycle that puts them at a disadvantage. Junior's people are unable to find gainful work, and many resort to alcohol abuse to cope with the stresses of poverty. Junior is angry that his people are denied so much, and when he sees his mom's name in his text book, something snaps.

Junior's school is so behind the times that students still use textbooks from thirty years prior. Information is so fast-paced these days that textbooks inevitably contain outdated information. Junior's school cannot afford new, up-to-date, and accurate textbooks every year-- apparently not even every thirty years! To Junior, this textbook bearing his mother's signature is a physical example of the institutionalized oppression the Spokane people suffer from. Junior is so mad at the textbook and his teacher, a man who benefits from and enforces this oppression, that he throws the book right in the teacher's face!