For years and years, both—Chris Confer and Marco Ramirez—worked as math resource teachers in high-poverty schools in Tucson, Arizona. They often worked together in a handful of schools where they provided mathematics professional development, workshops, and coaching for amazing, hardworking teachers. Over and over again they would see high-quality mathematics bubble up—for example, when a grade-level team at one school taught problem solving, or a group of teachers in another school used manipulatives to teach geometry. Through the school-based research that they have done for nearly two decades, it is clear that all children—even English language learners and children who live in poverty—can succeed in mathematics. They have learned that making sense of mathematics can change the culture of a school and sustain it. They have learned that teachers, coaches, and principals who intertwine their roles and together research math instruction realize what is possible for children to achieve. Finally, the chapter also provides an overview of this book.