We explored the cognitive development of physical knowledge for heating and cooling in a cross-cultural, mixed-gender sample of 270 children. Subjects were drawn from five age groups ranging in age from 4 to 13 years. Subjects were individually exposed to heating and cooling demonstrations, where after they were interviewed and assessed for their understanding of the phenomena in question. Results showed a clear developmental progression. The youngest children gave relatively unsophisticated explanations that focused on the source of heat but failed to explain the process itself. Slightly older children gave explanations that were characterized by a notion of movement (without a kinetic basis). The oldest children gave more sophisticated accounts of the process of heat transferral, which employed notions of convection, radiation, and conduction. This progression was unaffected by population group or gender, although a significant interaction between age and population was observed in the case of heating. The implications of these results for neo-Piagetian research are discussed. Some parallels between the developmental progression observed here and the historical development of scientific concepts of heat are noted.