Assessing a teacher's value: Too unreliable

09-10-2010

Opinion by Linda Darling-Hammond/New York Times Linda Darling-Hammond is the Charles E. Ducommon professor of education at Stanford University, where she is co-director of the Stanford Center on Opportunity Policy in Education.

Teacher evaluation was a fly-by operation when I was a high school English teacher 30 years ago, and it has improved little in most districts since. So I understand why there is such enthusiasm for evaluating teachers based on their students’ test score gains, now that such data are available. Evaluating and rewarding teachers primarily on the basis of gains on state test scores will discourage them from taking on struggling students. Unfortunately, as useful as new value-added assessments are for large-scale research, studies repeatedly show that these measures are highly unstable for individual teachers. Among teachers who rank lowest in one year, fewer than a third remain at the bottom the next year, while just as many move to the top half. The top rankings are equally unstable. In fact, less than 20 percent of the variance in teachers’ effectiveness ratings is predicted by their ratings the year before. This is why the National Research Council has said that this evaluation system "should not be used to make operational decisions because such estimates are far too unstable to be considered fair or reliable." (more…)

Also: New York Times

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