A teacher’s “value-added” is defined as the average test-score gain for his or her students, adjusted for differences across classrooms in student characteristics (such as their previous scores).Is teacher value-added a good measure of teacher quality?
That is the question three economists asked in a study, “The Long-term Impact of Teachers: Teacher Valued-Added and Student Outcomes in Adulthood.” A study that got quite a bit of media attention, but made me simply sigh because yet again the focus on good and bad teachers is all about students’ test scores. And so my answer to their question (based on my firsthand experience which is nothing like their number-laden data) is: no, no, no.
Their answer, of course, is the opposite of mine. And what to do about it, in their opinion, is to focus on what isn’t working rather than what is; in other words, fire as soon as possible the dead wood. From the Times article:
The authors argue that school districts should use value-added measures in evaluations, and to remove the lowest performers, despite the disruption and uncertainty involved.
“The message is to fire people sooner rather than later,” Professor Friedman said.
Professor Chetty acknowledged, “Of course there are going to be mistakes — teachers who get fired who do not deserve to get fired.” But he said that using value-added scores would lead to fewer mistakes, not more.
For a superb response to this see Maria Bustillos‘s “The Evil Economics of Judging Teachers” (via @JBell).