Why does little man get so upsetat school in the Roll of Thunder Hear My Cry?

Little Man throws his book on the floor because there are columns listing the condition of the book and the race of the student using it. The book is listed as being in "poor condition" and the race listed as "nigra". It is the first time the book has received both of these terms suggesting the book is no longer good enough for the white students but good enough for him.