Answer :
M. Hamel didn't scold Franz because that was the last when he would be teaching French to his students.
M. Hamel did not scold Franz even though he went late to class.
As it was the last day of French class in the school. From the next day onwards German language will be taught in school instead of French.
As the government had ordered to take German classes instead of French classes. So, M. Hamel was upset on hearing this news, so he let him to enter the class without scolding.