The Master of Triggernometry — J.T. Edson

Grattan, Texas is a bad place to get an education--and a worse place to be a teacher. One by one, the school masters and marms were given a choice: Take a permanent recess...or a bullet in the brain. In no time at all, the schoolhouse was empty. But now there's a new instructor in town. He's packing a six-shooter in his primer. He plans to teach a deadly lesson in revenge. And his name is Dusty Fog...