This policy brief examines standards-based approaches that hold promise for shaping a common vision of skilled teaching commensurate with the national goal of preparing all students for college and careers. Numerous studies confirm that teachers are the most significant school-based factor in improving student achievement, particularly for the most challenging students. Yet, while the current mantra is that "teachers make the difference", John Hattie, professor of education and director of the Visible Learning Labs at the University of Auckland, contends that this notion is not quite right. "Not all teachers are effective, not all are experts, and not all teachers have powerful effects on students... The important consideration is the ways that teachers differ in their influence on student achievement--what it is that makes the most difference?" "Some" teachers who undertake certain teaching acts with appropriately challenging curricula while also showing students how to think or strategize about the curricula produce powerful effects on student learning. Enough is known about effective teaching to act on a broad scale. Highlighted in this brief are successful prototypes for assessing teaching performance that have been shown to be effective in improving teacher performance, student learning, and teacher education. The pending reauthorization of the federal Elementary and Secondary Education Act (ESEA), currently known as the No Child Left Behind Act (NCLB), offers an opportunity to improve high schools by ensuring that systems are in place to build the teaching profession based on validated performance measures. The brief concludes with a set of policy recommendations to improve the consistency and quality of teaching in high schools. It calls for legislation, regulations, and incentives to help states and districts attend to the central role of human capital and the priority of fostering the expert performance of teachers in order to create high-quality learning environments for high school students. (Contains 45 endnotes.)