Christopher draws from both research and classroom experience to teach you how students' geometric thinking develops. In clear, approachable language, Christopher discusses the mathematical ideas likely to emerge on each page and helps you anticipate and understand students' likely answers. Through classroom stories from different grade levels, he models listening to, talking about, and delighting in students' ideas about shapes. Finally, Christopher gives you all the practical information you'll need to implement Which One Doesn't Belong? as a classroom routine, from how to launch rich discussions to how to create new sets to match your instructional goals. Reading the Teacher's Guide alongside your copy of Which One Doesn't Belong? will help you and your students discover the beauty of geometry and mathematics together.