This study looks at whether untrained observers are able to ‘read’ children's gestures, particularly those that do not match the child's speech. It also explores the frequent claim that gesture-speech mismatches can signal when a child is on the verge of learning a new concept. The diagnostic value of gestures is investigated by asking whether untrained adults are able to recognize this. Forty-two adult participants viewed twelve video clips of children's spontaneous explanations of a balance task. Each child produced only one type of spoken explanation, from four possible ones. However, half of the children conveyed a dierent explanation in their hand gestures. Participants assessed the children who produced gesture-speech mismatches as having more understanding of the concept than ‘matching’ children. Furthermore, they were more likely to assess these children as being on the verge of learning. Thus they were able to glean important information about the child's knowledge state from the children's gestures that was not indicated in speech alone.