Children and adults with Down syndrome vary widely in their achievements and interest in number skills and mathematics. There is only a small amount of research in the area and little that provides guidance for effective teaching methods and materials. Typically, the achievements of individuals with Down syndrome in number are at a lower level than their achievements in literacy. However, there is a wide range of progress and while some children find number difficult, other children with Down syndrome enjoy mathematics. When a pupil is interested, motivated and taught well, he or she may achieve at an age appropriate level in primary school. Research findings indicate that good teaching, using the children's strengths for visual learning, does promote learning and that children with Down syndrome follow similar stages of progression as typically developing children, although often with more steps and practice needed at each stage. This overview module reviews the development of number and maths skills in typically developing children, research on number and mathematics for children with Down syndrome, the implications for teaching and learning, inclusion in the mathematics curriculum, typical levels of achievement across the age range and the necessity for language teaching. This overview module links with the practical number modules for children aged 3-5 years, 5-11 (primary) and 11-16 years (secondary pupils). These modules contain discussion of the range of achievements, teaching methods and practical activities for each age group.