High-school is sort of the only place where people will go absolutely out of their way to help you with anything ever (teachers).
It's sort of weird. I pretty much hated everyone I ever met in high-school (I'm serious), but it's sort of weird to miss them. I guess you don't realise how much of a 'relationship' you have with people until they aren't there anymore (even if your relationship consists of snide comments at the locker bay).
I also think we have a tendency to glorify the past. School was probably the thing that was most depressing for me (the majority of it anyway), yet I still look back nostalgically and conveniently, I don't pay much attention to the horrible feelings that were had there, which heavily outweighed the good times hahaha.