The literature on effective schools emphasizes the importance of a quality teaching force in improving educational outcomes for students. In this paper, we use value-added methods to examine the relationship between a school’s effectiveness and the recruitment, assignment, development and retention of its teachers. Are effective schools effective because they happen to have recruited good teachers or do effective schools systematically recruit, develop and retain more effective teachers each year? Our results reveal four key findings. First, we find that more effective schools are able to attract and hire more effective teachers from other schools when vacancies arise. Second, we find that more effective schools assign novice teachers to students in a more equitable fashion. Across all schools we find that novice teachers are assigned lower achieving students than their more experienced colleagues at their school; however, the magnitude of this relationship is weaker in more effective schools. Third, teachers who work in schools that were more effective at raising achievement in a prior period improve more rapidly in a subsequent period than do those in less effective schools. Finally, we find that more effective schools are better able to retain higher-quality teachers. The results point to the importance of personnel, and perhaps, school personnel practices, for improving school outcomes.