Value-Added to What? How a Ceiling in the Testing Instrumental Influences Value-Added Estimation. Working Paper 2008-21

Value-added measures of teacher quality may be sensitive to the quantitative properties of the testing instruments upon which they are based. This paper focuses on the sensitivity of value-added to test-score-ceiling effects. Test-score ceilings are increasingly common in testing instruments across the country as education policy continues to emphasize proficiency-based reform. Encouragingly, we show that over a wide range of test-score ceiling severity, teachers' value-added estimates are only negligibly influenced by ceiling effects. However, as ceiling conditions approach those found in minimum-competency testing environments, value-added results are significantly altered. We suggest a simple statistical check for ceiling effects. (Contains 2 figures, 10 tables and 24 footnotes.)