One of the most intensely debated aspects of President Obama's "Race to the Top" fund for education, especially here in California, has been its insistence on a mechanism that would allow for teacher evaluations based on the performance of their students. It's a no-brainer as far as a lot of people are concerned, but teachers unions abhor it and California law specifically forbids linking teachers with student achievement, at least at the state level.

Now comes some interesting, and perhaps counterintuitive, news from Portugal, where the government recently began tying teacher pay to student achievement. A study released in May (and brought to our attention today by the Public Education Network) contains this stunner of a conclusion: "Overall, our results consistently indicate that the increased focus on individual teacher performance caused a sizable and statistically significant decline in student achievement."

That's right, students did worse when teacher pay was based on their performance. Go figure.

The study, by the Institute for the Study of Labor in Bonn, Germany, does contain solace for supporters of performance-based pay. Simply put, the Portuguese system might not be the best example of how to put together such a system, and the authors acknowledge that "teacher incentives ... may improve student achievement" if done well.

--Mitchell Landsberg