[MRM]

My family grew up reading the Little House Books out loud at bed time. In the book Farmer Boy, Almanzo Wilder (Laura Ingles Wilder's future husband) went to a one room school house. As in your great grandmother's story, there hadn't been a teacher able to finish the term for a couple of years because a family of bullies would beat the teacher to the point that he couldn't teach anymore. The older boys bragged to Almanzo that they were going to thrash the teacher soon. Almanzo warned his father, but Almanzo's father told him to mind his own business.

Sure enough a few days later the oldest boy in the family of bullies started acting up in class to provoke a fight with the teacher. The teacher called the boy forward to be disciplined. That was to be the sign that the boys were going to thrash the teacher. The other brothers got out of their desks in preparation of a mass attack and Almanzo was sure he was going to see his teacher killed.

The teacher calmly told the boys to return to their seats as he reached into his desk. As the boys rushed the teacher, he pulled a bull whip - Almanzo recognized it as his father's - and whipped the lead boy. As the lead bully fell back the teacher moved forward, whipping each would-be attacker ferociously until they ran out of the school. After the bullies were gone, the teacher put the whip back in his desk, dropped the lid, closed the school door, and retook his place at the blackboard without further comment.

The book doesn't mention any further school violence. This would have been in the 1870s.