The new report from the Brookings Institution, “Evaluating Teachers: The Important Role of Value-Added,” gives a nicely balanced presentation on the merits and pitfalls of using value added measures (VAM) in teacher evaluation. In Profit of Education I wrote, “a compensation system [based solely on a single, high-stakes test] is probably as nutty as a compensation system based zero percent on student outcomes–like he one we have.”
The new report reinforces the point that test measures, while imperfect, should play some role in teacher evaluation. And the authors make their point in a way that is both data-oriented and pretty funny. They write,
The correlation in test-based measures of teaching effectiveness between one school year and the next lies between .20 and .60 … with most estimates lying between .30 and .40. … The between-season correlation in batting averages for professional baseball players is .36.
Ask any manager of a baseball team whether he considers a player’s batting average from the previous year in decisions about the present year.