(This post also appears on Rick Hess Straight Up.)

In response to Monday’s post on the Nashville merit pay study, Gates Foundation research honcho and Harvard professor Tom Kane sent me a really thoughtful, incisive take on the study’s limitations. Tom, a good friend and one of the smartest folks in the business, is currently heading up the massive Gates research effort into teacher performance, evaluation, and pay.

Tom and I sometimes agree and sometimes have spirited disagreements on these issues, but on this one we’re reading from a shared hymnal. In fact, I thought his take so razor-sharp and succinct that I asked if I could share it, and he genially agreed.

Here’s what Tom had to say:

“It’s a well-done study of a not-very-interesting question. Merit pay for teachers could impact student achievement via three distinct routes: by encouraging teachers to work harder, by encouraging talented and skilled teachers to remain in teaching, by enticing talented and skilled people to enter teaching. The study was designed to answer a narrow question: can you make the average teacher work harder with monetary incentives? They did not report any results on the likelihood that more effective teachers would remain in teaching. Nor did they design the study to study entry into teaching.

We know there are huge differences in student achievement gains in different teachers’ classrooms. The authors confirmed that result. However, the impact of the specific incentive they tested depends on what underlies the differences in teacher effectiveness–effort vs. talent and accumulated skill. I’ve never believed that lack of teacher effort–as opposed to talent and skills–was the primary issue underlying poor student achievement gains. Rather, the primary hope for merit pay is that it will encourage talented teachers to remain in the classroom or to enter teaching. Although the jury is admittedly still out on it, this study provides no reason to question that hope.

Moreover, the study obviously says nothing about the potential impact of more meaningful tenure review. That, I think, is the most likely route of impact for teacher effectiveness policies.”