This is a study of the feasibility of teaching a causal theoretical understanding of biological inheritance to young children. The phenomenon of biological inheritance is a promising one in which to study children's learning of a system of knowledge, for it engages concerns over how understanding individual facts is related to having more broadly coherent frameworks of understanding. For those preschoolers who do not already understand biological inheritance, the construction of such an understanding could well entail a reorganization of which facts are at the causal core of their explanations of how and why offspring tend to resemble their parents. The present study was of a pre-test-intervention-post-test design involving tasks based on Johnson and Solomon (1997) and on Springer and Keil (1989) and building on Springer (1995). The intervention focused on three factors: first, children were motivated to seek change in their understanding (i.e. they were made aware that they lacked an explanation of why offspring resemble their parents); secondly, they were supplied with relevant facts (e.g. that babies come from their mothers’ bellies); and thirdly, they were presented with a conceptual peg (i.e. a rudimentary notion of genes) about which they could organize and better recruit those facts. Children who had taken part in the training were subsequently more likely to make adult-like judgments than those who had not.