It seems to be common knowledge that students act differently (or simply, worse) when they have a substitute teacher, therefore the "substitute teacher effect".
Everyone in the class behaves differently when Miss Smith is teaching.
I think it is the substitute teacher effect
When a struggling sports team fires their coach, and a new coach comes in and the team initially does really well.
Everyone is all smiles, the new coach tries new things, is fun and upbeat, and seemingly *changes the culture* so the team performs really well.....until they don't.
The few good games are due to excitement, and once the substitute teacher has to be a real teacher, fails spectacularly because he actually has to teach.
Boris: Oh fuck, you see how the new coach has turned this team around. I told you the old guy sucked.
Edgar: Meh, it is the Substitute Teacher Effect, come back to me in 3 months. Team is just playing well. New guy can't coach.
3 months later.....
Edgar: Team sucks, and coach looks really constipated.
Boris: Ya, you were right. Substitute Teacher Effect wins again.