Context: Policy makers have long used policy tools to influence various components of the education system. The passage of No Child Left Behind increased the federal role and the focus on student outcome measures. This change in the policy environment can affect not only teachers and teaching but researchers and research on teaching as well.…

This article examines a premise underlying teacher accountability policies, namely, that annual student learning gains can be attributed to individual teachers. After analyzing data collected in fourth- and fifth-grade reading and mathematics classes in 18 schools, the authors identify forms of instructional design that rely on multiple teachers.…