In this fourth edition of her signature resource, Marilyn presents her current thinking and insights and includes ideas from her most recent teaching experiences. Part 1, Starting Points, reflects the major overhaul of this book and addresses twenty-three issues important to thinking about teaching mathematics today. Part 2, Problem-Solving Investigations, opens with how to plan problem-solving lessons; followed by whole-class, small-group, and individual investigations organized into five areas of the curriculum: Measurement, Data, Geometry, Patterns and Algebraic Thinking, and Number and Operations. Part 3, Teaching Arithmetic, focuses on the cornerstone of elementary mathematics curriculum, offering ideas and assessments that build students understanding, confidence, and competence in arithmetic. In Part 4, Questions Teachers Ask, features Marilyn's responses to pedagogical questions she's received from teachers over the years.