Jim Manzi has some fascinating thoughts on evaluating teachers at the American Scene. Some summary outtakes:
1. Remember that the real goal of an evaluation system is not evaluation. The goal of an employee evaluation system is to help the organization achieve an outcome....2. You need a scorecard, not a score. There is almost never one number that can adequately summarize the performance of complex tasks like teaching that are executed as part of a collective enterprise....
3. All scorecards are temporary expedients. Beyond this, no list of metrics can usually adequately summarize performance, either....
4. Effective employee evaluation is not fully separable from effective management
When you zoom out to a certain point, all complex systems in need of reform start to look alike, because they all combine social, political, economic, and technical challenges, and the complexity, irrationality, and implacability of human behavior rears its ugly head at each step of the process. The debates about tactics and strategy and evaluation for reforming American education or US aid policy or improving health systems or fostering economic development start to blend together, so that Manzi's conclusions sound oddly familiar:
So where does this leave us? Without silver bullets.
Organizational reform is usually difficult because there is no one, simple root cause, other than at the level of gauzy abstraction. We are faced with a bowl of spaghetti of seemingly inextricably interlinked problems. Improving schools is difficult, long-term scut work. Market pressures are, in my view, essential. But, as I’ve tried to argue elsewhere at length, I doubt that simply “voucherizing” schools is a realistic strategy...
Read the rest of his conclusions here.