We investigated the developmental progression of reliance on object function versus object shape to extend novel words. In 3 experiments, 3-year-olds, 5-year-olds, and adults were presented with sets of objects consisting of a target, a same-shape/different-function match, a different-shape/same-function match, and a distracter. In Experiments 1 and 2, function was emphasized during the word learning phase and participants were given direct experience with the functions of target and test objects. In Experiment 3, function was emphasized both during the learning phase and when requesting a referent of the novel labels. Across all 3 experiments, 3- and 5-year-olds focused on shape while adults focused on function when extending the novel words. These results suggest a developmental change in the consideration of shape and function in lexical extension.