Full implementation of the Common Core State Standards for mathematics is still a few years away for many states. But district and school leaders are faced with many decisions now--from curriculum adoption to teacher professional development--that will influence the long-term effectiveness of this bold initiative. School leaders have a significant task in front of them, as they are key agents in ensuring that the Common Core fulfills its promise of transforming mathematics teaching and learning across the country. To lead an effective adoption of the standards, they need to know why a Common Core approach is different from what existed before, what mathematics instruction should look like, and how to support teachers throughout the implementation phase. The Common Core State Standards for Mathematical Practice require a new method of teaching. The authors suggest what to look for in your classrooms.