Think Tank Review, National Education Policy Center, Boulder Colorado. January 2011.
The Bill & Melinda Gates Foundation’s “Measures of Effective Teaching” (MET) Project seeks to validate the use of a teacher’s estimated “value-added”—computed from the year-on-year test score gains of her students—as a measure of teaching effectiveness. Using data from six school districts, the initial report examines correlations between student survey responses and value- added scores computed both from state tests and from higher-order tests of conceptual understanding. The study finds that the measures are related, but only modestly. The report interprets this as support for the use of value-added as the basis for teacher evaluations. This conclusion is unsupported, as the data in fact indicate that a teacher’s value-added for the state test is not strongly related to her effectiveness in a broader sense. Most notably, value-added for state assessments is correlated 0.5 or less with that for the alternative assessments, meaning that many teachers whose value-added for one test is low are in fact quite effective when judged by the other. As there is every reason to think that the problems with value-added measures apparent in the MET data would be worse in a high-stakes environment, the MET results are sobering about the value of student achievement data as a significant component of teacher evaluations.