[hatcravat]

I think you don't realize how politicized teaching has become. It doesn't matter if her students have good test scores: they all hate her. That one black mark is plenty for a determined administrator to get her fired. That a balanced review process would show see is a good teacher is simply immaterial. At least, that is how teachers see things.

Part of the reason you see so much backlash from teacher's unions against these initiatives (despite the fact that virtually all teachers acknowledge that some are better than others, and have a pretty fair idea who the worst ones are) is that they don't see this as a way to fairly evaluate teachers and improve the quality of education. Rather, they see it as a weapon to be wielded by school districts, school administrators, and angry parents ("Mrs. X told little Johnny (age: 17) where babies come from!" "Mr. Y is a member of $MARGINALIZED_SUBGROUP!" "Ms. Z believes something that is the current scientific consensus" "Mr. Q gave my son an A-") against unpopular teachers. It is an unfortunate fact of life, and even more unfortunate that so few are willing to admit it (especially here on HN, where the quality of discussion is usually above average).

We would probably have much greater buy-in from teaching unions if these evaluations were perceived as something other than politics as usual. Unfortunately, the proposals all seem to keep a some level of human involvement in the firing process (so only the very most outstanding teachers are immune to the usual political pressures). It's useful at this point to recall a bit of history: Teachers today are so hard to fire because they have tenure. Teaching unions successfully forced tenure the tenure system on school districts because school administrators of the past abused their authority to fire good teachers who happened to be politically unpopular.