On this note, and «[i] n sum, recent
research on value added tells us that, by using data from student perceptions, classroom observations, and test score growth, we can obtain credible evidence [
albeit weakly related evidence, referring to the Bill & Melinda Gates Foundation's MET studies] of the relative effectiveness of a set of teachers who teach similar kids [emphasis added]
under similar conditions [emphasis added]... [Although] if a district administrator uses data like that collected in MET, we can anticipate that an attempt to classify teachers for personnel decisions will be characterized by intolerably high error rates [emphasis added].