Randi's "VAM is a sham" epiphany

Weingarten, Bloomberg, and Klein announce an agreement on plan that would give N.Y. teachers bonuses based on the test scores of students at schools that have high concentrations of poor children. (New York Times)

I'm glad AFT Pres. Randi Weingarten has finally seen the light on VAM. Really I am.

For those unfamiliar with so-called Value Added Modeling, it's the statistical measure that judges teacher quality based on the test scores of their students. The formula for evaluating teachers, deciding their performance-based pay, or even whether they fired from their jobs, looks like this.

y = Xβ + Zv + ε where β is a p-by-1 vector of fixed effects; X is an n-by-p matrix; v is a q-by-1 vector of random effects; Z is an n-by-q matrix; E(v) = 0, Var(v) = G; E(ε) = 0, Var(ε) = R; Cov(v,ε) = 0. V = Var(y) = Var(y - Xβ) = Var(Zv + ε) = ZGZT + R.

It was obviously invented by some mad scientists and mathematicians working in the basement of the Gates Foundation. 

But the question I have for Randi is -- what are you going to do about all those VAM-based contracts you went along with, lobbied for and helped impose on thousands of teachers in districts like New Haven (which you hailed as a "model" and a "template"),  New York,  L.A., Cleveland, Detroit, and D.C.?

You may have changed you mind, but we will be living with VAM for years to come.