It is called VAM. Value-added-measurement, or value-added-modeling. It means measuring the effectiveness of teachers by the rise or fall of the test scores of their students.

Rachel M. Cohen, writing in The American Prospect, documents the slow but steady retreat from evaluating teachers by the test scores of their students. Only a few years ago, VAM was lauded by Secretary of a Education Arne Duncan as the ultimate way to determine which teachers were succeeding and which were failing; Duncan made it a condition of competing for Race to the Top billions, and more than 40 states agreed to adopt it; Bill Gates spent hundreds of millions of dollars promoting it; a team of economists led by Raj Chetty of Harvard claimed that the actions of a teacher in elementary school predicted teen pregnancy, adult earnings, and other momentous life consequences, and earned front-page status in the anew York Times; and thousands of teachers and principals were fired because of it.

But time is the test, and time has not been kind to VAM.

Cohen reviews the role of the courts, with some refusing to get involved, and others agreeing that VAM is arbitrary and capricious. She credits Duncan and Gates for their role in creating this monstrous and invalid way of evaluating teachers. The grand idea, having cut down many good teachers, is nearing its end. But not soon enough.