Why Were little man and cassie switched on the first day of school?

When the children receive their books the first day of school, Cassie sees how excited Little Man is to get a first grade reader because he cannot see the cover. Cassie picks up her book and begins to read it until she hears Miss Crocker yelling at Clayton Chester (Little Man) because he has asked for a book that is not dirty.

Little Man takes the book back to his desk, but when he opens it, sees something inside it that makes him throw it on the floor and stomp on it. Cassie looks inside her book and sees columns listing the book's condition and the race of the student for every year from 1922-1933. This is the first year that the book's condition is listed as "very poor" and the first time that the race of the student is listed as "nigra" instead of "white." As Miss Crocker is about to take the switch to Little Man, Cassie explains that her brother can already read and shows the teacher why he was angry. Miss Crocker tells Cassie that the books says "nigra" because that's what she is and orders her to sit down. Cassie tells Miss Crocker she doesn't want her book either. Miss Crocker takes the switch to both Little Man and Cassie.