This guy needs some character development.
He needs to learn one or two things from koro-sensei. A teachers job isn't only to make their students graduate with good grades. It's to build the foundation of their life to guide them how to live as a proper human.
I was thinking the same thing!!! At first I was like “lol serious teacher chad teacher” but now I feel like he rlly needs to understand the role that a teacher can play better. Who knows doe maybe the author intentionally did this to make some character development?