Mental Arithmetic is a highly differentiated, progressive series of books, proven to raise children's attainment (alone or in conjunction with the I Can Do Teacher's Guide which explains how to use the books as a scheme of work in schools). The series is based on ability (rather than age cohorts) so that books can be matched to the needs of every child (including supporting transition from KS1 to KS2 and KS2 to KS3). The books are also assessment-linked so that children can record their own progress and see their achievement build over time. Each book uses the same method of practising the 4 basic number operations (to keep skills sharp) and challenging children to do more complex one- and two-step problems involving logical thinking and application of knowledge previously introduced. Book 6 includes: positive and negative numbers, decimals, compound measures and conversions.