"Robert Green" wrote
Having close friends who are teachers, they would counter and say that
"performance based" ratings often end up really being "you've been here a
while and are too expensive to keep" sorts of games. It's not very easy
to
fairly rate a teacher because each year they get a new crop of kids with
varying degrees of intellectual competence.

Good teachers are always good, the bad ones are always bad, no matter who
the class consists of. Most of us have memorable teachers from our school
days and can attest to that. I've seen teachers fired (during my kid's
school years) and they deserved to be.