Children's conceptions of burning were explored through observation and discussion or a number of challenging phenomena. Analysis of written responses showed that children's conceptions are both specific and contextually based, and that there is little coherence in the use of any one conception across phenomena. Progression across the primary school years can be described, however, in terms of children's growing confidence with the idea of transformation of substances and the analysis relates this to a model based on changing commitments to the notion of substance defined by properties, rather than history. The conceptual trajectories described in the study are broadly consistent with previous studies of secondary school children.