Teachers who lose enthusiasm don't lose it because one day they wake up and think, "Man, I'm tenured now; fk all y'all I got mine." They lose it because of the vicious, dysfunctional attitudes taken toward teachers. That attitude being the one in which "we" expect teachers to be babysitters, guardians, mentors, and a variety of other things while at the same time facing a relentless assault on their competence, integrity, and wallets (lower pay, less support for classroom materials, etc.).

I put "we" in quotes because, clearly, I don't consider myself part of that group. Teachers, tenured or not, are as much victims as the students in this mess. They're all victims of--and this isn't going to be a popular opinion here, I bet--the very real, very destructive, anti-intellectual, anti-government, and anti-education strains of conservative politics that have increased sway in matters of the governance of education. This isn't a Democrat vs. Republican thing, either; as far as I'm concerned party affiliation is irrelevant (or, if you like, "both sides do it"). It is ideology that matters here. The destructive ideology I just described is the one most responsible for the problems we see in public schools, and that ideology is deeply entrenched in one party and becoming increasingly more entrenched in the other, to the point where the lines blur.

Yes, "we" treat our teachers pretty poorly. And they often succumb to the assault on them. But, it doesn't really matter if they lose enthusiasm over night or over a 10 year period. If they have lost their enthusiasm and are no longer performing their job to the satisfaction of their employer, there should not be a long complicated process to dismiss them.