The current research examined whether children could use certain metaconceptual criteria such as the range of explanation, non-ad hocness of explanation, empirical consistency, amd logical consistency to choose between competing accounts of physical phenomena. The tasks were constructed so that the conceptual content of the explanations to be evaluated was either consistent, inconsistent, or neutral with regard to children's prior knowledge. It was found that even 7-year-olds could use metaconceptual criteria such as the range, empirical consistency, and logical consistency theories when the theories did not violate their beliefs. However only older children (11-year-olds) showed a systematic preference for non-ad hoc theories over ad hoc ones. The findings are consistent with recent work in the philosophy of science showing that, in evaluating theoretical alternatives, scientists are influenced by their prior beliefs about the domain being considered. This research demonstrates that even young children share some of the cognitive underpinnings of scientific rationality that scientists do.