Book excerpt: Strengthen your mathematics lessons through collaborative planning Teaching by Design in Elementary Mathematics is a series of comprehensive professional development guides that help teachers investigate how students learn. Grounded in the latest research, this book is one of three volumes focused on grade-appropriate number and operations topics aligned with the Common Core State Standards. The capstone activity of each book guides the group through the co-creation and implementation of a prototype lesson. The teacher teams then evaluate the impact of the lesson on student learning and work together to revise it for maximum effectiveness. Through the process, teachers develop: Deeper content knowledge of important mathematical concepts Improved understanding of how students learn these mathematical ideas A stronger foundation for developing effective lessons and improving instruction Enhanced collaboration skills Each volume includes a large assortment of reproducible handouts as well as built-in facilitation notes. Teachers will also find helpful resources that address the issue of finding time for school-based professional development and teacher collaboration.