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[Susan notes: Stephen Krashen mentions something most people ignore: Value-added loses all credibility when one thinks about how how test scores can be pumped up without any increase in student learning.]

Submitted to USA Today but not published
01/26/2012

To the editor



"States weaken tenure rights for teachers" (Jan. 25) emphasizes the importance of evaluating teacher effectiveness.



A major problem is that these evaluations are often based on students gains on standardized tests, called "value-added" measures.



A number of studies have shown that value-added measures are very unstable: Teachers' ratings based on previous years are weak predictors of test scores at the end of a year with new students. A teacher who succeeds in boosting scores with one group will not necessarily succeed with others. Different tests can result in different scores for the same teacher.

Value-added evaluations also ignore the huge impact of factors beyond the teachers' control.



Finally, there are ways of pumping up test scores without student learning, including teaching test-taking strategies and making sure weak students don't take the test.



Nobody objects to teachers being evaluated on their effectiveness. Using gains on standardized tests is a bad way to do it.



Sources:

Not stable: Sass, T. 2008. The stability of value-added measures of teacher quality and implications for teacher compensation policy. Washington DC: CALDER. (National Center for Analysis of Longitudinal Data in Educational Research.) Kane, T. and Staiger, D. 2009. Estimating Teacher Impacts on Student Achievement: An Experimental Evaluation. NBER Working Paper No. 14607 http://www.nber.org/papers/w14607;

Different tests result in different value-added scores: Papay, J. 2010. Different tests, different answers: The stability of teacher value-added estimates across outcome measures. American Educational Research Journal 47,2.



Stephen Krashen, professor emeritus, USC


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