The Sensitive Task Of Sorting Value-Added Scores

Matthew DiCarlo:

The New Teacher Project's (TNTP) recent report on teacher retention, called "The Irreplaceables," garnered quite a bit of media attention. In a discussion of this report, I argued, among other things, that the label "irreplaceable" is a highly exaggerated way of describing their definitions, which, by the way, varied between the five districts included in the analysis. In general, TNTP's definitions are better-described as "probably above average in at least one subject" (and this distinction matters for how one interprets the results).

I'd like to elaborate a bit on this issue - that is, how to categorize teachers' growth model estimates, which one might do, for example, when incorporating them into a final evaluation score. This choice, which receives virtually no discussion in TNTP's report, is always a judgment call to some degree, but it's an important one for accountability policies. Many states and districts are drawing those very lines between teachers (and schools), and attaching consequences and rewards to the outcomes.

Let's take a very quick look, using the publicly-released 2010 "teacher data reports" from New York City (there are details about the data in the first footnote*). Keep in mind that these are just value-added estimates, and are thus, at best, incomplete measures of the performance of teachers (however, importantly, the discussion below is not specific to growth models; it can apply to many different types of performance measures).

Posted by Jim Zellmer at December 21, 2012 4:42 AM
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