Ex Post Teacher Quality

I really highly recommend Malcolm Gladwell’s article on quarterbacks and teacher quality in the current New Yorker. Unfortunately, I think that when talking about this important paper from Thomas J. Kane, Douglas O. Staiger, and CAP’s own Robert Gordon he gets a bit too entranced by the slightly mysterian notion that it’s impossible to identify effective teachers in advance. That may be true, but what the paper actually says is that our current certification methods don’t in fact do a good job of predicting teacher effectiveness.

One response to this could be to try harder to dream up a better method. But while it would probably be good to do some research into this issue, the Kane/Staiger/Gordon research also indicates that we could do a lot to improve the quality of instruction in our schools without identifying such a method. That’s because ex post evaluations of teacher effectiveness are pretty reliable predictors of future performance. In other words, if we look at the first few years of a teacher’s performance we can get a pretty good sense of how well she or he will fare over the course of her career.

The main policy implication of this is that we should be less strict about who we let into the classroom in the first place (since our current ex ante screening mechanism doesn’t work) and more strict and evidence-based about who we give tenure to (since we have good ex post screening mechanisms that we just don’t make much use of). A secondary implication is that it makes sense, at the margin, to commit resources to things that are more likely to draw applicants into the teaching profession through, e.g., higher salaries than on things like smaller class sizes. Basically, we should increase starting salaries and relax (or scrap) credentialing requirements, then make tenure decisions after a few years based on value-added test measures along with financial incentives to try to get the best performing teachers into the high-poverty schools and classrooms where they’re most needed.

Teacher quality is the internal-to-the-school variable that has the biggest apparent impact on students’ learning, and we actually have decent ways of measuring teacher performance. But we don’t actually do very much to put that information to good use. It’s a tremendous waste.