Principals, coaches, and teachers have an 80 percent drawer and a 20 percent drawer where they allot time for things that they see as more important and less important. The 80/20 Rule guides educators in determining how to use the very limited and precious resources of time, energy, and money to increase positive outcomes for students. The 80/20 Rule keeps the focus on what is most important: the research that teachers are doing to help students comprehend mathematics. This Rule provides an organizational structure to support decision making in schools. What economists call “cost-benefit analysis” is a useful strategy for successful school change. When anyone—a teacher, coach, or principal—makes a choice about what to do during instructional time, planning time, needs assessments, or budget meetings, the cost-to-benefit question must remain front and center. It is critical for coaches and principals to schedule time in classrooms, working alongside teachers, keeping their eyes on the prize of high-quality classroom instruction.