In the context of growing awareness of young children's capabilities, and debates about the nature of their reasoning in science, this study set out to explore the ways in which reception children make sense of classroom experiences in science. A particular challenge of the study was to develop appropriate and productive approaches to investigating young children's developing thinking. The first phase of research, reported in this paper, concentrated on the topic of electricity. A series of case studies was undertaken to examine children's learning in a classroom context. Classroom sessions were video recorded and transcribed to examine the development of children's practical competence in circuit making, and interviews were carried out to elicit children's views about electric circuits. Analysis of the classroom sessions revealed children's growing competence in circuit making through their self-directed efforts. The interviews prompted predictions and explanations that were not offered spontaneously. Responses indicated a range of models of the circuit and forms of explanation for what was happening in the circuit. The relationship between children's practical competence, predictions and explanations was not straightforward. Analysis revealed marked differences in models of the circuit and forms of explanation in children with the same levels of practical competence. This has important implications for the ways in which children's views are assessed.