Evaluating Value-Added Models for Teacher Accountability

Abstract

Value-added modeling (VAM) to estimate school and teacher effects is currently of considerable interest to researchers and policymakers.Recent reports suggest that VAM demonstrates the importance of teachers as a source of variance in student outcomes.Policymakers see VAM as a possible component of education reform through improved teacher evaluations or as part of test-based accountability.They are particularly intrigued by VAM because of the view that its complex statistical techniques can provide estimates of the effects of teachers and schools that are not distorted by the powerful effects of such noneducational factors as family background.Although VAM holds great promise, it also raises many fundamental and complex issues.Some of these issues may appear arcane, but the reasonableness of the findings of VAM studies depends on them.If these issues are not adequately addressed, VAM is likely to misjudge the effectiveness of teachers and schools and could produce incorrect generalizations about their characteristics, thus hampering systematic efforts to improve education.Unfortunately, investigation and discussion of the issues raised by the use of VAM in education have been fragmented and limited.In addition, much of the discussion is unpublished, and the practical import of these concerns when VAM is applied to student achievement remains largely unclarified.In this monograph, we clarify the primary questions raised by the use of VAM for measuring teacher effects, review the most important recent applications of VAM, and discuss a variety of the most important statistical and measurement issues that might affect the iv Evaluating Value-Added Models for Teacher Accountability validity of VAM inferences.Although the document focuses on measures of teacher effectiveness, many of the points discussed here also apply to measures of school effects.The monograph should be of interest to policymakers who are considering the use of VAM for teacher evaluations or accountability.It will also be of interest to researchers who are looking to use VAM to understand teachers or looking for ways to improve VAM models.This research was done within RAND Education and was