Evaluating teachers: look at the data, please

A new report by the Measures of Effective Teaching project and supported by the Bill & Melinda Gates Foundation looks into the accuracy of classroom observations, as compared to and combined with other things such as value-added measures. The results are too long to discuss in a blog post, but one point caught my eye.

Much of the report compared the “predictive power” of different evaluations. That is, it looked at how likely any given type of evaluation (classroom observations, rigorous student surveys, value-added measures, or a combination), was to predict student gains on state tests in math and reading.

The graph that caught my eye compared the predictive value of a combination of these evaluations vs. the predictive value of graduate degrees or years of experience, the two measures used most often in determining raises and layoffs. For graduate degrees and experience, the predictive value was slight; but for the combined evaluation measures, the predictive value was noticeably more significant. Students who had the top 25% of teachers (as identified by the combined evaluation) gained roughly between one and five more months’ worth of learning than those who had teachers in the bottom 25%.

The point is this: a combined evaluation, using multiple measures of a teacher’s effectiveness including value-added measures, was more effective in identifying the teachers who boosted students learning than any of the traditional measures such as experience or degrees. And the report showed elsewhere that a combined evaluation was more effective than any single evaluation measurement.

My takeaway? Please, let’s use data in evaluating teachers. It doesn’t just have to be numbers — for instance, those rigorous student surveys did a good job, too. But as we argued in Building a Better Evaluation System, value-added models have a place in evaluating teachers as part of a system of multiple measures.

It’s time to build a better evaluation system. It won’t be perfect, but the evidence is mounting that it will be better than what we’ve got. –Rebecca St. Andrie