Children use properties of information and epistemic states of others to socially evaluate informants in pedagogical contexts. Recent studies have shown that in pedagogical contexts, children expect teachers to provide information to support accurate inference. Do children simply prefer teachers who provide more information, or do they rationally expect teachers to provide the “right amount” of information? Here we present a computational model of social learning that incorporates the cost of acquiring information and a series of experiments with children (5- and 6-year-olds) to test its predictions. Children observed two teachers who either provided a “minimal” amount of information or “exhaustive” information about a multi-function toy to a naïve learner. Consistent with the predictions of the model, children’s preferences rationally reflected the informativeness of the teachers’ demonstrations, the cost of observing the demonstrations, and even the learner’s epistemic state. Taken together, the results suggest that learners can use information provided by others to not only learn about the target object but also to rationally evaluate others in order to guide their future choices of informants.