Teacher Effects as a Measure of Teacher Effectiveness: Construct Validity Considerations in TVAAS (Tennessee Value Added Assessment System)

This paper examines the validity of measures of teacher effectiveness from the Tennessee Value Added Assessment System (TVAAS). Specifically, we consider the following claims regarding teacher effects: that they adequately capture teachers' unique contributions to student learning; that they reflect adequate standards of excellence for comparing teachers; that they provide useful diagnostic information to guide instructional practice; and, that student test scores adequately capture desired outcome of teaching. Our analyses of the TVAAS model highlight potential weaknesses and identify gaps in the current record of empirical evidence bearing on its validity. Introduction The Tennessee Value Added Assessment System (TVAAS) is a statistical methodology designed to evaluate the influence that school systems, schools, and individual teachers on student learning. It is arguably the most prominent example of the “value-added” approach in state accountability systems. The statistical machinery behind TVAAS, developed by William Sanders at the University of Tennessee, implements a mixed-effects model, applied to longitudinal standardized test score data across several subject areas, to estimate the effects of schools and individual teachers on student