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A big story today is a report out by the Economic Policy Institute that criticizes value-added scores for teacher performance evaluations. Kevin Carey at The Quick and the Ed puts this challenge to the authors of the paper regarding how much weight should be placed on these measures in teacher evaluations:

The Economic Policy Institute’s new brief, which details the many concerns with and limitations to current value-added measures, says that 50% is “unwise.” However, despite EPI’s litany of concerns with value-added, the authors, who include Diane Ravitch, Helen Ladd, and Linda Darling-Hammond, conclude that: “Used with caution, value-added modeling can add useful information to comprehensive analyses of student progress and can help support stronger inferences about the influences of teachers, schools, and programs on student growth.”

But if 50% is unwise, what is EPI’s number? The paper doesn’t specify and calls for experimentation among districts. Experimentation is good. But I’d also like to see EPI’s authors and other value-added critics put their best number on the table. I doubt they will, though, because for many, that number is very close to 0%. And defending that number would be much more difficult than pointing out the flaws in value-added.

Kevin also discusses the shortcomings of value-added in a broader perspective:

Value-added measures of teacher effectiveness are not all that great…. But, and this is an enormous caveat, everything else we currently use is worse. A teacher’s years of experience, their education credentials, their certification status, the prestige of their college or their college GPA, even in-class observations. None of these measures does as good of a job at predicting a student’s academic growth as a teacher’s value-added score. Yet, we continue to use these poor proxies for quality at the same we have such passionate fights about measures of actual performance.

Carey’s two points together highlight an important question: if the weakness of the connection between value-added scores and teacher effectiveness means we should place a low weight, say 10%, on those scores for teacher compensation, than what does that tell us about the weight that should be placed on seniority and credentials? The answer has to be much less than 10%, since the evidence suggests those are far worse measures. Test scores representing 10%, and everything else that is currently used to decide pay representing less than that would be a significant improvement over the status quo. That would just mean a pay scale that is about 80% flat.

You know what, maybe you should just be reading The Quick and the Ed instead of me.

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