Every new skill takes practice to get right. This practical new book recognizes a simple but important truth — "You can't learn math without making mistakes." It shows you how to take mistakes and turn them on their head, using them to students' advantage. Each of the twenty-two activities offered in the book focuses on important ideas in mathematics. By examining comic strips, letters to a fictitious math expert from confused students, and sample student work containing mistakes, young learners explore typical math errors, reflect on why they're wrong, and move toward a deeper understanding of numbers and math.