I guess that's why the teacher is currently full of guilt in the present; despite him standing up for himself to his bullies he's still the one who will get in trouble since he fought back.
that, and the fact that she 100% let it get to the point where he was accused by the class, after he was accused by both teachers, and then to the point of him being beaten by
everyone else in the class, only to turn around and...what looks like, put several of them in the hospital.
Also - notice that Glasses Sensei
only stepped in the moment
he was about to hit a girl. Yes, she ran in shouting "what are you kids doing? Stop that everyone!" and then....they both just stood there watching.
Neither of them moved to pull kids off of him when they were taking turns aiming their feet at his ribs and kidneys.
To the end, they failed him at every single turn, both on the macro and the micro.