Right-sizing the Classroom: Making the Most of Great Teachers

This CALDER Center paper examines the value of strategically assigning disproportionately larger classes to the strongest teachers in order to optimize student learning in the face of differential teacher effectiveness. The rationale is straightforward: Larger classes for the best teachers benefit the pupils who are reassigned to them; they also help the less effective teachers improve their instruction by enabling them to concentrate on fewer students. But just how much of a difference could manipulating class sizes in this way make for overall student learning and access to effective teaching? This study performs a simulation based on North Carolina data to estimate plausible student outcomes under this approach.

In the North Carolina data, there is a very slight tendency to place more students in the classes of effective teachers; but still only about 25 percent of students are taught by the top 25 percent of teachers. Intensively reallocating eighth-grade students—so that the most effective teachers have up to twelve more pupils than the average classroom—may produce gains equivalent to adding roughly two-and-a-half extra weeks of school. Even adding a handful of students to the most effective eighth-grade teachers (up to six more than the school’s average) produces gains in math and science akin to extending the school year by nearly two weeks or, equivalently, to removing the lowest five percent of teachers from the classroom. The potential impacts on learning are more modest in fifth grade, where the large majority of teachers are in self-contained classrooms.

Results show that this strategy shows an overall improvement in student access to effective teaching, yet gaps in access for economically disadvantaged students persist. For instance, disadvantaged eighth-grade students are about 8 percent less likely than non-disadvantaged peers to be assigned to a teacher in the top 25 percent of performance. This gap in access changes little in spite of the policy putting more students in front of effective teachers— because the pool of available teachers in high-poverty schools does not change under this strategy. Thus, this policy alone shows little promise in reducing achievement gaps.