There seems to be an assumption by many in this thread that performance appraisals in the private sector are unbiased, fair, and accurate. In general they aren't. Cronyism/favoritism are a part of performance appraisals either explicitly or implicitly.
If you want a good appraisal, make your boss look good, make your "team" look good, get your team to like you, and bust your AXX to achieve hard and soft measurements related to your role.
The difference in teaching is that nearly all of the people who really know what you do are minors. Are we really ready for performance appraisals based on the feedback of 3rd graders?
I still think every teacher should in conjunction with administration create a professional development document at the end of each school year that identifies strengths and weaknesses. It would also identify actions to be taken in the upcoming 12 months to strengthen weaknesses. It would identify hard measurements based on the kind courses to be taught the next year and historic performances. These could include test scores, but they would only be a small part.
As in most things where we want to perform well, we need to identify process goals and then honestly assess how we did against those goals. If we are achieving the process goals but the achievements are not as good as desired, then you re-evaluate the process goals together with administration.
Everyone doesn't need to have the same goals or be assessed on the same criteria. Everyone should be seeking to get better.
This process allows administrators to encourage high performers to take on the toughest assignments.
We've got to stop acting like every teaching role is the same and should be evaluated by the same metrics.
We've also got to lose the adversarial environment that is too present in the world of education. We can't continue with the teacher vs administration approach. I think 95% or more of most faculties want to do a great job including administrators. We would be much better off working as a team towards goals tailored to our situations.
As it stands now, I don't think most teachers have a performance improvement plan unless they have already received poor performance ratings. That's crazy. We can all improve. Why do we wait until there's a problem to worry about improving?
We don't need standardized test scores to accomplish this. We need trust.