Recently, teacher evaluation has become a major focus in educational policy debates and research efforts. This increased attention to teacher evaluation has raised questions about the relationship between evaluation and student outcomes. Rivkin, Hanushek, and Kain (2005) and others have demonstrated with value-added research that there are sizeable differences among teachers in their ability to help students learn at high levels--not just across schools but within schools. These differences lie at the heart of the current approaches to measuring teacher effectiveness through teacher evaluation. The results of these evaluations will be used in many districts and states for accountability purposes to make high-stakes decisions about teachers. Evaluation may be a tool to help teachers improve, but school leaders often lack training in how to use evaluation results to guide teachers toward professional growth. However, both outcomes of evaluation--for accountability and for improvement--rely on the same foundation for making decisions: reliable and valid evidence about teacher performance and student learning. Questions to Support Alignment are appended. (Contains 1 figure and 2 tables.)