The charter sector has grown dramatically since its beginnings in Minnesota almost a quarter of a century ago. Today, an estimated 2.5 million children attend approximately 6,400 charter schools across the country, and all but 8 states have charter laws in place. The expansion of the sector has been accompanied by an increase in public commentary…

A growing body of research confirms the long-held belief of parents, school administrators, and policy makers that teachers are the key component to a good education and that there is substantial variation in teacher quality. This research differs fundamentally from prior work on teachers by focusing directly on differences in student learning…