Value added and its uses: Where you stand depends on where you sit

In this policy brief we argue that there is little debate about the statistical properties of value-added model (VAM) estimates of teacher performance, yet, despite this, there is little consensus about what the evidence about VAMs implies for their practical utility as part of high-stakes performance evaluation systems. A review of the evidence base that underlies the debate over VAM measures, followed by our subjective opinions about the value of using VAMs, illustrates how different policy conclusions can easily arise even given a high-level general agreement about an existing body of evidence. We conclude the brief by offering a few thoughts about the limits of our knowledge and what that means for those who do wish to integrate VAMs into their own teacher-evaluation strategy.