It didn't help his mood any that the incoming Grade 7 class was made up of the most fiendish lot of kids ever inflicted on a suffering world, with about as much music in the lot of them as in an average turnip. Their mothers were worse. The principal of the school was an idiot, always on his case grumping about discipline.
and then the class he's teaching next year:
As a responsible, married man, life was good. It felt surprisingly right to be settled, and not like a cage at all. To add to his satisfaction, Phil found his work at the school more interesting every year as he experimented with new ways to excite kids about music. His Junk Band experience came in useful many, many times.
The reason for the sea change in the quality of students isn't especially miraculous but we cannot expect Phil to want to admit to why that might be. Lynn likes to describe him as having a mercurial temperament but to me, he's just another stupid, self-absorbed son of a bitch letting his commitment issues boil over onto other people. It is, sadly, human nature to not especially want to look back and see that he'd made a huge, ugly fool of himself by attaching too much importance to a certain phenomenon and getting wound up and angry merely because he has to consider the rights and opinions of other people instead of being a solipsistic no-account all his life. Admitting that he'd gotten into a pointless war with his superiors and parents, let discipline go to Hell and deliberately shortchanged a group of children because he was busy throwing a tantrum and feeling sorry for himself is not something we can or should expect of him. He's Jim and Marian's child; self-awareness and decent, respectable behaviour are beyond him.