I've been thinking how this guy managed to get accepted as a teacher there...
I mean, the head staff in that school isn't that fond of hearing there's any bulllying in there, so i'm sure the head staff won't accept any teacher that have even a small connection to bullying in the past. Unless the plot device made the whole staff don't know about any of the male protag past and only the students know about it (tho it still just a small part of it).