Volume 18, Issue 2
October, 2010
MCALLEN AFT NEWS
MAKING A DIFFERENCE
VALUE-ADDED SCORE
BASED ON ACHIEVEMENT TESTS
Policy-makers may be drawn to the simplicity of reducing teacher evaluation to a “value-added” score based on achievement tests, but they are neglecting an expanding body of educational research that shows this seeming simplicity comes at the expense of accuracy.
Educational historian Diane Ravitch, in her latest “Bridging Differences” blog entry (http://blogs.edweek.org/edweek/BridgingDifferences/2010/10/dear_deborah_you_asked_what.html), cites a new study from the Annenberg Institute for School Reform at Brown University that finds value-added assessments of teacher effectiveness are at best a “crude indicator” of teachers’ contributions to students’ academic outcomes. Author Sean Corcoran, a professor of educational economics at New York University, concludes: “The promise that value-added systems can provide a precise, meaningful and comprehensive picture is much overblown. Teachers, policy-makers and school leaders should not be seduced by the elegant simplicity of value-added measures. Policy-makers, in particular, should be fully aware of their limitations and consider whether their minimal benefits outweigh their cost.”
Corcoran notes that, in theory, value-added models attempt to define a teacher’s unique contribution to students’ achievement that cannot be attributed to any other current or past student, family, teacher, school, peer, or community influence. However, Corcoran points out, in practice it is exceptionally difficult to isolate a teacher’s unique effect on academic achievement.
“The successful use of value-added requires a high level of confidence in the attribution of achievement gains to specific teachers,” he says. “Given one year of test scores, it’s impossible to distinguish between the teacher’s effect and other classroom-specific factors. Over many years, the effects of other factors average out, making it easier to infer a teacher’s impact. But this is little comfort to a teacher or school leader searching for actionable information today.”
“Not all subjects are or can be tested, and even within tested subject areas, only certain skills readily conform to standardized testing,” he says.
State tests are often predictable in both content and format, and value-added rankings will tend to reward those who take the time to master the predictability of the test.”
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