Wednesday, September 1, 2010

Value Added?

"Value-added modeling" has been in the news a lot lately.  A way of judging teacher performance through student testing that attempts to adjust for socio-economics and other factors, it is viewed by some as a more factual representation of teaching ability.  Instead of merely looking at student scores for one year, it tracks performance of individual students over multiple years, and aligns predictions of student performance with actual performance in a teachers' class.  Thus students on track to make a certain level of progressed are averaged against how students tend to do in a teacher's classroom.  Sounds good, right?

Well, the Economic Policy Institute, a liberal Washington think-tank has a new policy brief out that challenges the efficacy of this type of modeling.  Some pretty high-powered co-authors, including the infamous Diane Ravitch. Choice quote:
A study designed to test this question used VAM methods to assign effects to teachers after controlling for other factors, but applied the model backwards to see if credible results were obtained. Surprisingly, it found that students’ fifth grade teachers were good predictors of their fourth grade test scores. Inasmuch as a student’s later fifth grade teacher cannot possibly have influenced that student’s fourth grade performance, this curious result can only mean that VAM results are based on factors other than teachers’ actual effectiveness.

Read the whole thing.

p.s. EPI is a think-tank after all, and have an axe to grind.  fwiw

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