The International Association for the Evaluation of Educational Achievement's (IEA) mission is to enhance knowledge about education systems worldwide, and to provide high-quality data that will support education reform and lead to better teaching and learning in schools. In pursuit of this aim, it conducts, and reports on, major studies of student achievement in literacy, mathematics, science, citizenship, and digital literacy. These studies, most notably Trends in International Mathematics and Science Study (TIMSS), Progress in International Reading Literacy Study (PIRLS), International Civic and Citizenship Education Study (ICCS), and International Computer and Information Literacy Study (ICILS), are well established and have set the benchmark for international comparative studies in education. The studies have generated vast datasets encompassing student achievement, disaggregated in a variety of ways, along with a wealth of contextual information which contains considerable explanatory power. The numerous reports that have emerged from them are a valuable contribution to the corpus of educational research. The IEA Research for Education series represents a further effort by IEA to capitalize on unique datasets, so as to provide powerful information for policymakers and researchers. Each report focuses on a specific topic and is produced by a dedicated team of leading scholars on the theme in question. Teams are selected on the basis of an open call for tenders; there are two such calls a year. Tenders are subject to a thorough review process, as are the reports produced (Full details are available on the IEA website). This sixth volume in the series is concerned with teacher quality and educational outcomes. Regarded as the most vital school resource, teachers are key to understanding the "black box" of education. To that end, the current volume examines the link between teacher effectiveness and student outcomes from several different perspectives. Especially important in this research is understanding whether better teachers can mitigate the known deleterious effect of low socioeconomic status. Literature on the links between social class and achievement abounds; however, questions remain concerning the role of the teacher and teaching quality in this relationship. To begin a study on the importance of teacher effectiveness, the authors draw on data collected over 20 years by the IEA's TIMSS. Although student outcomes, namely, achievement, figure prominently in this work, the authors use a wide array of contextual information to bring their narrative to life. [For volume 5, see ED599011.]