Most education reformers agree that effective teaching is defined by improving student learning, but they disagree on how to measure teacher effectiveness and how to use those measurements to improve teaching. Thus far, most of the policy debate on teacher effectiveness has focused on using test scores to implement merit pay or to fire teachers, but those strategies alone will not lift teacher performance on a large scale. In order to improve high school teaching, educators and policymakers must first invest in solid, objective ways to measure a teacher’s effectiveness. Currently, many experts believe that the best method is to use “value-added” analysis, a statistical method described in more detail in this brief.