Most of the time when Grant is standing in front of his students at school he's wielding his terrifying ruler or using it on their poor little hands and noggins because he is so irritated with them all the time. One time he even yells at a girl who cries when he talks about her cousin, Jefferson, being executed.
However, the very last image in the novel is Grant turning to his students and crying:
"I went up to the desk and turned to face them. I was crying." (31.93)
By turning to face his students and really looking at them like his equals instead of like his victims, Grant is showing everyone that he is finally opening up. His tears show that he's allowing himself to feel something, and the fact that he's being honest with his students shows that Grant has learned a lesson before dying.