Do you sometimes start to teach a mathematics concept and feel like you are staring at a sea of bewildered faces? What happens when you discover that students previously learned a calculation trick or a mnemonic that has muddied their long-term understanding? When "rules" seem to change from year to year, teacher to teacher, or school to school, mathematics can seem like a disconnected mystery for students. Clear up the confusion with a mathematics whole-school agreement! Expanded from the highly popular "Rules That Expire" series of NCTM articles, this essential guide leads educators through the collaborative step-by-step process of establishing a coherent and consistent learner-centered and equitable approach to mathematics instruction. Through this work, you will identify, streamline, and become passionate about using clear and consistent mathematical language, notations, representations, rules, and generalizations within and across classrooms and grades. Importantly, you will learn to avoid "rules that expire"--tricks that may seem to help students in one grade but hurt in the long run. Features of this book include the following: (1) Effective working plans for sustainability; (2) Barrier-busting tips, to-dos, and try-it-outs; (3) Practical templates and checklists; and (4) PLC prompts and discussion points. When teachers unite across grades, students hit the ground running every year. Take the next step together as a team and help all your students build on existing understanding to find new success and most importantly, love learning and doing mathematics.