The relationship between gesture and speech predicts readiness to learn.

The gestures that accompany speech encode meaning differently from speech. Gesture relies on visual and mimetic imagery to convey an idea holistically, whereas speech conveys meaning discretely, relying on codified words and grammatical devices. Nonetheless, the information conveyed in gesture and in speech can overlap a great deal. Consider, for example, a child asked first whether the amount of water in two identical glasses is the same, and then whether the amount of water in one of the glasses changes after it is poured into a low, wide dish. The child says that the amounts of water are initially the same but differ after the pouring transformation – the child is a non-conserver. When asked to explain this answer, the child focuses on the height of the water in both speech and gesture, saying ‘it's different because this one's low and that one's tall’, while gesturing the height of the water in the dish and then in the glass. The child thus conveys the same information in gesture and speech: a gesture–speech match.

There are, however, times when gesture conveys different information from speech. Consider another child (also a non-conserver) who gives the same explanation as the first child in speech but a different explanation in gesture. She produces a two-handed gesture representing the width of the dish, followed by a narrower one-handed gesture representing the width of the glass. This child focuses on height in speech but width in gesture. She has produced a gesture–speech mismatch.

Children who produce mismatches on a task have information relevant to solving the task at their fingertips. The child has noticed (albeit not consciously) that the dish is short and wide but the glass is tall and narrow, a potentially important insight into conservation. Such a child might therefore be particularly receptive to instruction in conservation. Indeed, when non-conservers are given instruction, the children who produce gesture–speech mismatches before that instruction are more likely to make progress on the task than children who produce matches. This phenomenon is robust, found in learners of all ages on a variety of tasks taught by an experimenter (5- to 9-year-olds learning a balance task; 9- to 10-year-olds learning a math task; adults learning a gears task), or learned in relatively naturalistic situations (toddlers learning their first word combinations; school-aged children learning a mathematical concept from a teacher).

What makes gesture such an effective learning tool? There are several possibilities. First, gesture is based on a different representational format from speech. Whereas speech is segmented and linear, gesture can convey several pieces of information all at once. At a certain point in acquiring a concept, it might be easier to understand, and to convey, novel information in the visuospatial medium offered by gesture than in the verbal medium offered by speech.

Second, gesture is not explicitly acknowledged. As a result, gesture can allow speakers to introduce into their repertoires novel ideas not entirely consistent with their current beliefs, without inviting challenge from a listener – indeed, without inviting challenge from their own self-monitoring systems. Gesture might allow ideas to slip into the system simply because it is not the focus of attention. Once in, those new ideas could catalyze change.

Third, gesture helps to ground words in the world. Deictic gestures point out objects and actions in space and thus provide a context for the words they accompany. Gestures might, as a result, make it easier to understand words and also to produce them.

Whatever the process, there is ample evidence that the spontaneous gestures we produce when we talk reflect our thoughts – often thoughts not conveyed in our speech. Moreover, evidence is mounting that gesture goes well beyond reflecting our thoughts, to playing a role in shaping them.