Little Man got upset because the teacher give him a textbook that was beaten up and it had racist words in the first page of the textbook saying 'nigro'.
Mama took the textbook Little Man had shown her and put a blank piece of paper and glued it on top of the words it had on. Even though she can get in trouble for doing that.
Mr. Granger fired Mama for teaching the students things that weren't in the textbook. But also was fired for the incident that Mama did with Little Man's textbook. She was mostly fired because of the Wallace boycott.