Studies of student achievement generally do not consider the effect of school size, or do so peripherally. Using the production function approach and data from Baltimore (Maryland) public elementary schools, school size is shown to have a negligible effect on the performance of these students on standardized achievement tests. Consistent with other studies, the importance of the socio-economic status of the students and the lack of a positive effect of school input measures such as the teacher/pupil ratio and expenditure per pupil is borne out in these results.