11 : Value - Added Assessment of Teachers : the Empirical Evidence

The Tennessee Value-Added Assessment System (TVAAS) employs a sophisticated statistical methodology to estimate the aggregated yearly growth in student learning, as reflected in changes in test scores in five tested academic subjects. It assumes that changes in test scores from one year to the next accurately reflect student progress in learning. By tracking progress and linking it to schools and teachers, the model asserts that the educational effects of these schools and teachers can be evaluated. Estimates of aggregated gains are used as indicators of how effective teachers and schools have been in raising student performance. Yet, the model’s empirical base is weak and fails to document adequately its efficacy as a teacher evaluation instrument. It remains unclear how other variables that may affect achievement as much as teacher effectiveness will determine the evaluation results. Much more research is needed in order to rationally judge the system’s strength and weaknesses.