How did Mama get fired

The reasons were filled with racism and bigotry. Mama is teaching about slavery and all the atrocities that took place. Granger and one of the Wallace brothers have come to Mama's class and hear Mama talk about slavery. Her explanations don't follow the official white account that is written in the textbook. The men smirk and demand to know why Mama is not teaching properly. Mama explains that the "facts" in the book are lies. Granger replies, "I expect you'd best just forget about teaching altogether...then that away you'll have plenty of time to write your own book." Mama has been fired.