When we meet Paul, he has managed to get on the nerves of all his teachers, and this has gotten him suspended from school. Since we really only hear Paul's side of the story, it's not surprising that the teachers come off badly. They talk with "rancor and aggrievedness" (1.3), and they attack him "without mercy" (1.4).
The teachers definitely abuse their authority by bullying Paul. But at the same time, we see that they're personally hurt by Paul's dislike of them. The English teacher he recoils from "could scarcely have been more hurt and embarrassed had he struck at her" (1.3).
It's worth pointing out that Willa Cather was teaching high school (and had been for many years) in Pittsburgh when she wrote this story. Maybe she's drawing from some personal experience, here.