I’m confused how is him being a teacher helping him?

He's making sure people (mainly the kids) stay alive and become proper hunters so they can be of use to him in the future during the end of the world
Or at least that's what I gathered

This^^^^^^^
Plus since he was "suspicious" he didn't really had any say in that matter. It was a mean to watch his every move (HE EVEN HAD A TRACER LIKE A CRIMINAL LMAOO). Also being close to his father/the director will help finding his younger self as stated in his "teacher" contract lol
(Source: How I understood it-)