Numbers can be represented in a variety of ways--through pictures, diagrams, symbols. Each representation highlights different features of the number and the number system. This study aims to explore pupil understanding of number both within and across representations. A computer environment (suite of programmes) was created within which representations could be generated and manipulated. This study focuses on one of the programmes within which activities were developed for pupils in years 1, 2 and 3 of English primary schools (ages 5 to 8 years). The results were analysed across year groups and across attainment levels. The study found that not all representations are equally well understood. Reading figures accurately, often comes before an understanding of place value. Over the first three years of schooling there is improvement in understanding all representations although the number line and the beads seem to cause some difficulties. An ability to count in tens and ones is associated with greater understanding of many representations. (Contains 1 table and 11 figures.)