Previous investigators have found significant relations between children's early spontaneous gesture and their subsequent vocabulary development: the more gesture children produce early, the larger their later vocabularies. The questions we address here are (1) whether we can increase children's gesturing through experimental manipulation and, if so, (2) whether we can increase children's vocabulary through our impact on child gesture. Our study included 15 children (8 males) who were 17-months-old and at the one-word stage of language development at the start of the study. We conducted an 8-week intervention study in which we experimentally manipulated children's gesture production once a week over the course of 6 weeks. We then assessed their vocabulary at a follow-up visit 2 weeks after the last training visit.

Children were randomly assigned to one of 3 conditions. In the gesture instruction condition, the experimenter provided object labels accompanied by points to target pictures and then instructed children to point to the target picture. There were 2 control conditions in which children were not instructed to gesture. In the gesture-input control condition the experimenter provided the spoken target labels accompanied by points. In the speech-alone control condition the experimenter only provided spoken target labels. Our results show that children instructed to gesture, gestured significantly more during the experiment than children not instructed to gesture. Further, this condition effect of increasing child gesture extended outside the experiment into children's spontaneous interactions with their parents. Second, we find a significant indirect effect of instruction on child vocabulary that operates through child gesture. This study furthers our understanding of the relation between early gesture and spoken vocabulary development and suggests that gesture plays a role in early word learning.