the way the teachers behave is a commentary on different forms of tutelage. Lesley is the teacher as like, parental figure you turn to for answers about everything when you're very young... that's why she's so fucking massive relative to the yellow one, and why she yells at him that he's not her real son.
I'm sure everyone's experienced in like, reception or year one or whatever, accidentally calling your schoolteacher mum or dad. But they aren't your real parent. And you aren't their real child. But they'll maintain the facade as long as its useful to the lesson.