Just how meaningful are those value-added ratings?

From Diane Ravitch:
The studies of value-added measurement keep on coming, and the findings usually show what an utterly absurd idea it to think that teacher quality can be judged by student test scores. The results of that study, led by Marianne P. Bitler, an economics professor at the University of California, Irvine, have been presented at multiple academic conferences this year. The authors found that teachers’ one-year “effects” on student height were nearly as large as their effects upon reading and math.

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