What is the real reason that Mr.Granger has Mrs. Logan fired? What justification does he give for firing her?

Kaleb Wallace, another man, and Harlan Granger enter Mama's classroom. They say that they are representing the School Board and watch as Mama continues the history lesson she that she had been teaching about slavery. Mama talks about its cruelty and the economic benefits that the ruling class got from the free labor of others. Mr. Granger opens a student's book, with the paper pasted on the front cover, and accuses Mama of teaching things that aren't in the book, which was approved by the School Board. He fires her. Mama later tells Papa, Mr. Morrison, and Big Ma that she has lost her job, and says that it is their way of getting back at the family for shopping in Vicksburg.

thay fierd mama for reveng fo the boycot that thay did

I would agree with you jill, but however, didn't she get fired because of T.J. I thought that he cheated, which is the reason why she got fired.