Abstract
Departmentalized instruction, in which teachers specialize in one or more core subjects and instruct multiple groups of students in a day, has become increasingly prominent in elementary schools. Departmentalization involves a potential trade-off: specialized assignments exploit teacher comparative advantage across subjects but introduce coordination costs across teams of teachers instructing common students. Using 8 years of data from Massachusetts and a difference-in-differences design, we estimate the effects of departmentalization on student achievement. Overall, we find that departmentalization has positive effects in English language arts (ELA) and science and either null or positive effects in math. Consistent with prior findings on teacher specialization, teachers are less effective when specializing in math and no more effective in ELA than when teaching self-contained classrooms. Rather, the improvements are driven by departmentalized schools assigning teachers to their stronger subjects.