Randi Weingarten has come out in opposition to value-added modeling (VAM), the statistical measure that judges teacher quality based on the test scores of their students. This is great news! As I have often written here, VAM is Junk Science. It also is the centerpiece of Race to the Top, which makes the absurd assumption that good teachers produce higher test scores. Researchers have shown again and again that test scores–including their rise or fall–says more about who is in the class than teacher quality, and they reflect many other factors, including class size, peers, school leadership, prior teachers, curriculum, etc. Furthermore, VAM places too much emphasis on testing and leads to a narrowed curriculum, teaching to the test, gaming the system, and cheating. Teaching cannot be reduced to an algorithm.

To those tempted to chastise her for changing her mind, I say we should welcome and salute anyone with the courage and insight to give up a previously held position in the face of evidence. A few years ago, I changed my mind about things I once believed, like the value of school choice and high-stakes testing. Now, let us hope that others who support VAM see the light.

This morning’s Politico Education says:

“NEW TACTIC ON TEACHER EVALUATIONS: Randi Weingarten, president of the American Federation of Teachers, is launching a campaign against using value-added metrics to evaluate teacher effectiveness. Her mantra: “VAM is a sham.� That’s a notable shift for the AFT and its affiliates, which have previously ratified contracts and endorsed evaluation systems that rely on VAM. Weingarten tells Morning Education that she has always been leery of value-added “but we rolled up our sleeves, acted in good faith and tried to make it work.� Now, she says, she’s disillusioned.

“– What changed her mind?Weingarten points to a standoff in Pittsburgh over the implementation of a VAM-based evaluation system the union had endorsed. She says the algorithms and cut scores used to rate teachers were arbitrary. And she found the process corrosive: The VAM score was just a number that didn’t show teachers their strengths or weaknesses or suggest ways to improve. Weingarten said the final straw was the news that the contractor calculating VAM scores for D.C. teachers made a typo in the algorithm, resulting in 44 teachers receiving incorrect scores — including one who was unjustly fired for poor performance.

“– What’s next? The AFT’s newly militant stance against VAM will likely affect contract negotiations in local districts, and the union also plans to lobby the Education Department.”