With the material discussed in the previous chapter, we seem to have identi­ fied an area where children’s knowledge shows a stepwise progression in content but is theoretically structured from the start. However, is this true with all contexts where heat is transferred? Up to now, we have restricted our attention to contexts where the transfer of heat implies a rise in temperature. However, during changes of phase-like melting and solidifying, evaporating and condensing, heat is transferred but temperature remains constant. Yet the variables which science deems relevant to changes of phase and the mechanisms that are called upon are equivalent to the ones identified in the previous chapter for temperature change.