Health education is a part of the primary school science curriculum in France. Teachers often consider sexuality education and sexually transmitted diseases prevention as a topic they cannot teach without the help of partners. This paper is an account of a research carried out to study the representations of primary school pupils (Key Stage 2, French children, from 9-11) about HIV/AIDS and to analyse the impact of an educational programme on these representations. The Programme was based on a socio-constructivist approach to learning. It aimed to modify pupils' representations through regular teacher's activities and interventions of health educators. The results indicate that after the intervention, pupils' scientific knowledge was more precise, and communication about HIV/AIDS between members of the family improved. The representations shifted from a sense of powerlessness and fatality towards a sense of the possibility of acting to forestall infection. Nevertheless, the impact of the intervention was weaker on under-privileged pupils.