In February 2012, the "New York Times" took the unusual step of publishing performance ratings for nearly 18,000 New York City teachers based on their students' test-score gains, commonly called value-added (VA) measures. This action, which followed a similar release of ratings in Los Angeles last year, drew new attention to the growing use of VA analysis as a tool for teacher evaluation. Newspapers that publish value added measures no doubt relish the attention they generate, but the bigger question is whether VA should play any role in the evaluation of teachers. Advocates argue that the use of VA measures in decisions regarding teacher selection, retraining, and dismissal will boost student achievement, while critics contend that the measures are a poor indicator of teacher quality and should play little if any role in high-stakes decisions. The debate over the merits of using value added to evaluate teachers stems primarily from two questions. First, do VA measures work? Second, do VA measures matter in the long run? The authors address these two questions by analyzing school-district data from grades 3-8 for 2.5 million children, linked to information on their outcomes as young adults and the characteristics of their parents. The authors find that teacher VA measures both work and matter. First, they find that VA measures accurately predict teachers' impacts on test scores once they control for the student characteristics that are typically accounted for when creating VA measures. Second, they find that students assigned to high-VA teachers are more likely to attend college, attend higher-quality colleges, earn more, live in higher socioeconomic status (SES) neighborhoods, and save more for retirement. Commentaries from four experts on the study's implications for teacher policy are included. (Contains 2 figures.)