Why not link teacher pay to test scores?

Lisa Guisbond:

Have your kids ever gotten an A for work that you, or they, didn’t think was worthwhile? Something like that happened recently with Education Secretary Arne Duncan.
Education historian and New York University Professor Diane Ravitch gave him an A for effectiveness at getting buy-in for linking teacher evaluations to student test scores and a D- for pushing bad ideas. I would forgo the A and lower the grade to an F for pushing ideas that are destructive.
Why destructive? At first blush, rewarding teachers for higher student test scores seems reasonable to many people. The second and third blushes are the problem.

The National Center for Fair & Open Testing.