Teacher evaluation (and unions for that matter) are kind of my life's work right now.
The real issue is that the value-added measures that are typically used to measure teacher effectiveness have significant statistical problems. When you add to that the issue that current evaluation systems do not really measure the variables that have been proven to be necessary for high quality teaching and learning, it becomes a serious mess. And, when you add in the fact that administrators in schools do not have the time or expertise to put toward meaningful evaluation, you find us where we are right now.
Until the money is invested in a good evaluation system with sufficient time and training for administrators to use it properly, unions are going to fight against changes to tenure, evaluation and seniority rights. The current climate is one where most of the dismissals (except for ones related to obvious misconduct) are political and retaliatory and not based on sound evidence of ability to do one's job.
