This text is designed to help coordinators and teachers of mathematics in primary schools to plan and develop an appropriate, differentiated scheme of mental mathematics activity to support numeracy and other mathematical work throughout the primary years. Moving beyond simplistic notions of recall and memorising, the authors explore: the multi-dimensional range of mental mathematics; the various representations and images that assist learning; and the development of language to promote the discussion of mathematical ideas. For non-specialist mathematicians and students in training the book provides a resource of ideas to help pupils to become efficient "in-head" workers, as promoted in the National Numeracy Strategy. Each chapter discusses the context and theory underlying particular aspects of work before setting out a range of suggested activities for each year group.