The purpose of this article is to investigate the relationship between school instructional climate and students' fifth-grade mathematics and reading achievement, with a particular emphasis on norms for practice consistent with differentiated instruction. Using data from a stratified random sample of Michigan elementary schools, we employed multilevel structural equation modeling to test our hypothesis. Our results confirmed that school norms for teaching practices consistent with differentiating instruction were positively and significantly associated with differences among schools in mathematics and reading achievement. The results are important for educators seeking knowledge about school characteristics and instructional practices associated with improved student achievement.