My perspective is different from most here. I teach in a private high school. We have elements of merit pay at my school. I also accept less pay than my public colleagues because I'm willing to do that for the sake of fewer headaches, and for the chance to design my own curriculum. From my perspective, I'm dubious of my public school colleagues dismissing merit pay or any other education reform aimed at providing a metric for evaluating teachers. We all know one of the biggest (not the only) problem with our education system is bad teachers. We must arrive at a system that rewards good teachers and drives out or trains up bad ones. Standing in the way of this progress is antithetical to progressivism.