Wednesday, September 22, 2010

Teacher performance pay

Here is the WaPo piece on the teacher performance pay experiment that I described in an earlier post and that is being presented at the Ford School this afternoon.

The experimental design here is solid but there are some issues of interpretation that stem directly from the nature of the study design.

1. Only volunteer teachers were randomized. Whether one should expect the effects of performance incentives to be higher or lower for volunteers than non-volunteers is not clear a priori but using volunteers makes the politics of doing a random assignment study much easier. The importance of this issue also depends on the take-up rate, which as I recall was higher than you might think but not 100 percent by any means.

2. This is a temporary program. That means that incentives to invest in being a better teacher are limited, as they pay off only in the short term. The numbers at play in the study are not trivial but also not large relative to, say, the cost of going back to college to get a subject area degree.

3. As Rick Hanushek notes in the article, by design the study looks only at current teachers. One important effect of an ongoing regime of performance pay might be to change the mix of people who become teachers in good ways. This study cannot pick up that effect.

4. The treatment is just performance pay. There is no mentoring or other treatment. If teachers are going to figure out how to do better, they are on their own with the literature. Knowing something about the literature, I know that is problematic. But it is not clear that combining performance pay with the sort of additional treatments mentioned in the article, such as mentoring, would work. For example, the randomized trial that the Dept. of Education funded on additional mentoring for new teachers did not produce clear positive results.

I should note in relation to the last point that things are very different in many developing countries. There the effort margin is often quite important. In some countries, for example, teacher absence rates are shockingly high. Performance pay might well get them to show up, and showing up would likely improve test scores.

A side point: why is Rick Hanushek the only person quoted who is identified as having political beliefs? The Hooover Institution where he works is labeled "conservative leaning" while the fellow from the teacher labor cartel is not given any politics, nor are the people from the federal government, nor is anyone else.

Hat tip: Dann Millimet

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