Plainsong by Kent Haruf:
Guthrie grabbed him once more but he jerked away and then the boy swung and hit Guthrie at the side of the face, and then he whirled and ran away down the hallway and on outside, headed toward the parking lot. Guthrie watched him through the hallway windows. The boy got into his car, a dark blue Ford, and drove off, screeching across the parking lot and out of sight. Guthrie stood in the hallway and made himself breathe until he was calm again. The side of his face felt numb. He supposed he would feel it more later on. He took out a handkerchief and wiped it across his mouth and felt something on his tongue and spat it into the handkerchief and looked at it. A bloody piece of a tooth. He put it in his shirt pocket and wiped his mouth again and put the handkerchief away. The he opened the door to the classroom and entered in on an immediate natural quiet. The students were all watching him.
Take out your books, he told them. Read until the bell. I don’t want to hear anything more from any one of you today. You can finish your speeches tomorrow.