Special education law has mandated that students with disabilities be served in the "least restrictive environment" possible. This often takes the form of an inclusive classroom, or a general education classroom where students with disabilities learn alongside their non-disabled peers. In some cases, inclusive classrooms are co-taught by a general education teacher and a special education teacher who share planning and instructional responsibilities. The logic behind co-teaching is intuitively appealing. Co-teaching reduces the student-teacher ratio, and the presence of two educators, each with distinctive expertise, should make it easier to connect students at a range of abilities to grade-level content. In this article, the authors examine a decade of test scores for students in Massachusetts, where co-teaching has experienced rapid growth, and find positive effects on academic achievement for students with and without disabilities in the years they are enrolled in co-taught classes.