Jimmy points me to a sequence of posts (Analyzing Released NYC Value-Added Data Parts 1, 2, 3, 4) by Gary Rubinstein slamming value-added assessment of teachers.
A skeptical consensus seems to have arisen on this issue. The teachers groups don’t like the numbers and it seems like none of the reformers trust the numbers enough to defend them. Lots of people like the idea of evaluating teacher performance, but I don’t see anybody out there wanting to seriously defend the numbers that are being pushed out here.
P.S. Just to be clear, I’m specifically addressing the problems arising in value assessment of individual teachers. I’m not criticizing the interesting research by Jonah Rockoff and others on the distribution of teacher effects. It’s a lot easier to estimate the distribution of a set of parameters than to estimate the parameters individually.