The Primary Mathematics U.S. Edition series of elementary math textbooks and workbooks is meant to be part of a system of learning in which adult supervision and independent practice go hand in hand. The main feature of this series is the use of the Concrete > Pictorial > Abstract approach. Students are provided with the necessary learning experiences beginning with the concrete and pictorial stages, followed by the abstract stage to enable them to learn mathematics meaningfully. This approach encourages active thinking process, communication of mathematical ideas and problem solving. This helps develop the foundation students will need for more advanced mathematics. The above extract is from Preface of Primary Mathematics U.S. Edition (reproduced with the permission of the publishers).  The workbooks are consumable and should be used in conjunction with the textbooks. They contain the exercises the student does independently. Answers or answer keys for Primary Mathematics U.S. Edition textbooks and workbooks are found in the teacher's guides and home instructor's guides. Answer keys booklets are also available for purchase - one for Primary 1-3 and one for Primary 4-6.