This article reports on research into the potential of interactive multimedia to develop K–1 students' understanding of fractions. Children participating in the research used three different types of interactive multimedia designed to further their understanding of mathematics. Students who had participated in the intervention developed a more sophisticated understanding of fractions than a comparison group. The strongest advance in students' understandings came when they worked with 'manipulable multimedia', which permit young learners to manipulate mathematical representations that had been assigned to them. Less effective were forms of multimedia which direct learners to complete prescribed tasks, or which call on the learners to generate their own mathematical representations.