Working in the foundation stage requires careful planning and effective use of new experiences, so that teachers can help children to extend their skills, develop their confidence and build on what they already know. They can also set challenges, as Bruner commented: "Any idea or body of knowledge can be presented in a form simple enough so that any particular learner can understand it." This was demonstrated delightfully when it started snowing during a science lesson with a class of 3 and 4 year-olds. The authors use a constructivist approach to learning and teaching: using elicitation and intervention to expose and address misconceptions and planning new experiences to develop understanding. In this article, the authors show how teachers can take the opportunity of a snowfall to develop very young children's science ideas about melting and freezing. (Contains 3 figures.)