The gestures children produce predict the early stages of spoken language development. Here we ask whether gesture is a global predictor of language learning, or whether particular gestures predict particular language outcomes. We observed 52 children interacting with their caregivers at home, and found that gesture use at 18 months selectively predicted lexical versus syntactic skills at 42 months, even with early child speech controlled. Specifically, number of different meanings conveyed in gesture at 18 months predicted vocabulary at 42 months, but number of gesture+speech combinations did not. In contrast, number of gesture+speech combinations, particularly those conveying sentence-like ideas, produced at 18 months predicted sentence complexity at 42 months, but meanings conveyed in gesture did not. We can thus predict particular milestones in vocabulary and sentence complexity at age by watching how children move their hands two years earlier.