This is a very complicated matter and I can only talk about my own classroom, but this article gave the best analogy I've heard that explains the situation I'm in.
Suppose you are foreman of a project and your pay will depend on how well your crew has done the work. The rating, however, is not based on the job from start to finish but on how much better your job is than that of the jobs the crew worked on last year under other foremen. The projects were different from yours and took place in different locations. Now you know what the so-called value-added models for teacher performance evaluation are like.
"Grading teachers: What's the best way?
The method the state wants to use certainly isn’t"
By VICTOR L. WILLSON
Feb. 13, 2010, 7:02PM
I won't go on any longer but teaching has now become very depressing and it makes a person want to retire RIGHT NOW!