As economies of scale increase, school districts, by means of policy strategy, trade class size against salary incentive for teachers. This idea is developed and related to district-level achievement through an explanatory, structural equation model. The model is tested on data on student achievement in 102 Colorado school districts. The results show that the model is moderately successful for explaining reading achievement in grades 5, 6, 11, and 12. However, factors not yet included in the model are believed to have strong effects.