This book guides teachers in the appropriate use of calculators in math classrooms in grades 3-8. This resource is organized into two parts. Part One addresses the broad range of classroom teachers' questions and concerns about using calculators for teaching mathematics. Issues covered include: (1) How can calculators support helping children learn mathematics?; (2) How can teachers assess student learning if they are using a calculator?; (3) Is it important for all students to have access to the same model of calculator?; (4) Should students be allowed to use calculators during tests?; and (5) How can calculators help develop children's number sense? Part Two features a collection of classroom-tested activities for using calculators in math lessons, all chosen for the purpose of developing children's number sense and problem-solving abilities. For each activity students engage with a task, explore the mathematics embedded in it, and explain their answers and the reasons for them. (KHR)