[bramcohen]

Looking at the correlation in students between year to year makes clear what's going on - http://garyrubinstein.teachforus.org/2012/03/06/analyzing-re...

There's such a high correlation between an individual student's score from one year to the next, and the number of data points is so small, that trying to tweeze out the teacher's contribution in a statistically meaningful way is fairly hopeless.

What I'd like to see are correlates with a teacher's own scores on the tests of the material they're supposed to be teaching (oh you think they all can get perfect scores easily? Hah!) and whether teachers banned from giving homework do any worse, and whether dumping the enforced curriculum in favor of letting students study at their own pace makes any difference. Given how little what the teachers actually do seems to make, it would be logical to at least dump the things which make school dull and unpleasant.