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If a teacher evaluation system is to be valid, schools and districts must develop a definition of teaching (evaluative criteria) and then use instruments and procedures to assess teachers according to those criteria. Any evaluation system requires that teachers do certain things: For example, they may allow administrators or peers to observe them while teaching, they may complete a portfolio of lesson plans, they may submit letters they have written to parents. Taken together, what teachers do as part of the evaluation procedures should provide evidence of all the evaluative criteria. For example, if “establishing an environment of respect and rapport” is included as an essential criterion of teaching, then how will teachers demonstrate their skill? How should teachers organize their procedures to enable an evaluator to judge their classroom environment?
Some teaching standards are written in such a manner that they cannot be evaluated reliably. This relates to the fact that only behavior can be assessed. States of mind, beliefs, values, and some kinds of knowledge are invisible until they are revealed in behavior. Consider, for example, the NBPTS standard: The teacher is “committed to students and their learning.” Although no one would disagree with the values embodied in such as statement, how can teachers validly demonstrate such a commitment? There would be indicators, to be sure (for example, a teacher might go to considerable lengths to locate alternative materials for a student needing them, or tutor students during the lunch period). But the commitment itself is a mental state that evaluators can only infer from the teacher's actions.
Some of the evaluative criteria, no doubt, are of the type that a principal or a peer might observe in the classroom during a teaching episode. An observer could determine whether the environment in the classroom was a respectful one, both between the teacher and the students and among the students. Or an observer could analyze the questions the teacher asked for their level of cognitive challenge.
But other possible criteria (such as communicating with families, or collaborating with colleagues) are invisible in the classroom; these criteria require other types of documentation. How can teachers demonstrate their skill in all the diverse aspects of the complex activity of teaching? What would count as evidence, and how should it be evaluated?