This book contains a carefully selected and adapted set of lessons from NCTM's Navigations series, with a special emphasis on incorporating the Effective Mathematics Teaching Practices in NCTM's Principles to Actions. Teachers of PK-2 students can use these activities to engage their students in exploring, thinking, connecting, discussing, justifying, and advancing in their mathematical understanding and confidence. Each of the 10 Activity Gems includes the following elements: An overview of how the lesson can help PK-2 students develop their mathematical knowledge and abilities, with lists of goals to achieve and all needed materials A detailed three-part lesson plan-designed to Engage, Explore, and Extend-including questions a teacher can pose, possible responses and challenges that students may present, and ways to continue the learning beyond the activity Activity sheets, classroom images and figures, and any other necessary materials, all available both in an appendix and in downloadable and printable form at NCTM's more4U website Working together, these Activity Gems give PK-2 teachers the tools to use purposeful discussion and productive struggle to guide their students toward both conceptual understanding and fluid problem solving.