The main argument against this is that teachers might be penalized for teaching in rough schools instead of lily-white. middle class, suburban schools. I don't

The main argument against this is that teachers might be penalized for teaching in rough schools instead of lily-white. middle class, suburban schools. I don't see a reason the system couldn't be set up to normalize the schools based on what the metrics turn out to be. I guess each school would get a performance index that would act as a coefficient for the teachers there. E.g., the metric is a test score, and one school consistently scores near the national average, while another is 10 points lower. The teachers at the lower school would have their evaluation bumped 10 points because of the index. That way we'd be comparing apples to applies. It could actually incentivize teachers to move into more difficult schools if the index were a little over done so that they were rewarded slightly more for the same effort. Their effort would theoretically move the school's average into line with the national average, then they'd be evaluated/paid the same -- they could then move on to the next problem school, and improve that.