How does the ability to discriminate between relevant and irrelevant explanations develop? In two experiments, 120 4-year-olds, Kindergarteners, and 2nd graders were presented with statements in three categories: true-relevant (“Cars have engines that turn gasoline into power”), true-irrelevant (“Cars have radios that play music”), and false (“Cars have rockets that speed them up”). Participants were asked whether each statement was helpful or not helpful for understanding what makes cars go. Experiment 1 showed that when children younger than 2nd grade are presented with explanations one-by-one, they reject false explanations but endorse both true-relevant and true-irrelevant explanations as helpful. In contrast, Experiment 2 showed that when true-relevant and true-irrelevant explanations are directly contrasted, children as young as 4 identify the relevant explanations as more helpful. Ongoing studies examine which kinds of contrasts are most helpful and whether there are ways to encourage children to create these contrasts on their own.