Across the educational systems of the world, few issues have received more attention in recent years than the problem of ensuring that elementary and secondary-school classrooms are all staffed with adequately qualified teachers (Mullis, et al., 2000; OECD, 1994, 2005; Wang, et al., 2003). Even in nations where students routinely score high on international exams, the issue of teacher quality is the subject of much concern. This is not surprising. Elementary and secondary schooling is mandatory in almost all nations and children are legally placed in the care of teachers for a significant portion of their lives. It is widely believed that the quality of teachers and teaching are among the most important factors shaping the learning and growth of students. Moreover, this impact goes beyond student academic achievement. Across the world, observers routinely tie the performance of teachers to numerous, larger societal goals and problems—economic competitiveness and productivity, juvenile delinquency, moral and civic culture, and so on. In addition, the largest single component of the cost of education in any country typically is teacher compensation. Along with a general consensus among many nations that the quality of teachers and teaching is a vital resource, there is accordingly much concern surrounding how equitably this resource is distributed within educational systems. Indeed, some nations suffer from an apparent paradox—that despite an overall overproduction and oversupply of new teachers, there nevertheless appear to be substantial numbers of students without access to qualified teachers. Such concern has resulted in a steady stream of commissions, reports, and studies all targeting teacher quality as one of the central problems facing school systems. In many nations this concern has resulted in new legislation and policy. Foremost among these have been widespread efforts to increase the entry standards and preparation requirements for teachers. Hong Kong, for instance, initiated in 1997 an “all graduate, all trained” policy requiring new primary- and secondary-school teachers to have bachelor’s degrees and to be professionally trained. In Japan there has been an active reform movement to increase teacher preparation requirements and increase evaluation and accountability of teachers. In the United States this concern surfaced within a massive new piece of legislation in 2002, the federal law known as the No Child Left Behind Act, which in addition to new standards for student achievement, set a new and unprecedented goal— to ensure that elementary and secondary students in the United States are all taught by highly qualified teachers. In addition to, or perhaps because of, recognition of its importance, the issue of teacher quality also is a source of debate and disagreement in many nations.