Policymakers nationwide continue to wrestle with a basic question: At what grade level should students move to a new school? In the most common grade configuration in American school districts, public school students make two school transitions, entering a middle school in grade 6 or 7 and a high school in grade 9. This pattern reflects the…

In recent years, a consensus has emerged among researchers that teacher quality matters enormously for student performance. Students taught by more-effective teachers learn substantially more over the course of the year than students taught by less-effective teachers. Yet little is known about what makes for a more-effective teacher. Most research…