There is nothing wrong with observing a class and providing a measure of a teacher's effectiveness. I've written about this many times before on the Forum, citing my own experiences. What is at issue in all teacher evaluation is who is doing the evaluation and how is it done.

At the risk of repeating myself, I don't see any problem with evaluation of teaching provided it is cohesive, inclusive and undertaken by people who know enough about the process and are not afraid to confront poor practice - but from the perspective of appropriate methodology. Far too often, teacher evaluation is nothing more than an excuse to find reasons for dismissal or non-payment of contractual benefits.

The SAFEA contract for FTs, for all its flaws, is quite clear on evaluation and probationay periods.