Many schools are in some stage of implementing differentiated instruction, with some already in what Carol Tomlinson describes in "The Differentiated School" as "second order change," where the entire school practices differentiation. In high-performing schools, differentiation has proved to be an effective instructional strategy; in classroom environments with low-performing learners and students with disabilities, it can have even greater impact. Principals new to differentiation need to know and fully understand the concept and how it can be used to refine classroom instruction in all content areas. This understanding of schoolwide application across disciplines enables effective teachers to enhance student learning outcomes. One of the challenges for principals is ensuring teachers obtain the necessary training, planning time, resources, and support to implement differentiation successfully in their classroom settings. Principals must encourage teachers to think beyond the traditional classroom environments and adopt differentiated practices in every classroom. This article presents nine practices that should help every school in transitioning to a "second order" school.