Caving to pressure from US Education Secretary Arne Duncan, Governor Jay Inslee is urging legislators to amend Washington state's teacher and principal evaluation rules to take into account student test scores. At risk is a waiver that gives the state control over how to spend $40 million in No Child Left Behind money.

Legislators will probably accede. But Democrats should say "No." And for two distinct reasons.

First, tying teacher evaluations to student test scores is just bad policy based on bad science. It incentivizes teachers to teach to the test at the expense of the broader educational curriculum and experience. And, there is simply no reliable evidence that student test scores provide a relevant metric for evaluating teacher performance. Indeed, a recent analysis of "value added" data (measuring the value a teacher adds to their students' standardized test performance) from the New York City Public Schools found little or no correlation between teacher performance from one class to another or from year to year. Indeed, across classrooms and time, the value added data was almost entirely random.

The second reason to reject the federal mandate—and just as important—is that Washington's current teacher evaluation system is the result of a lengthy and intense collaboration between teachers, principals, administrators, and lawmakers. We have spent years both debating a teacher evaluation system and building a consensus to sustain it. Overhauling teacher evaluations once again, at the whim of federal regulators, would be unnecessarily disruptive to both our schools and our political process.

Yes, $40 million in federal money is at stake. Perhaps we'll lose some control over how to spend it. But that is a small price to pay for maintaining the integrity and stability of the teacher evaluation system we have struggled hard to put into place.