This article explores relationships between designing and making in the work of children within the age range 5-11 when engaged in practical modelling tasks. The notion of the model is explored from the perspective of concrete representations. It is suggested that concrete models may be used as hypotheses from which to test ideas about the nature of the world. From this perspective, models may be seen to provide crucial platforms for learning. A wide range of sources has informed the article, and these embrace ideas on Hypothesis Theory drawn from linguistic research, as well as historical sources which trace the evolution and development of stimuli for model-making activity. A creative basis for modelling is explored such that a conclusion is reached in which design is seen as an expression of the modelling of possibilities.