This study examined the effect of lexical aspect on children's imitation accuracy of English tense-aspect morphology. Thirty-five typically developing children, ages 2;4 to 3;1, imitated sentence-pairs in which the same regular verb was used once in an activity (skip on the rug) and once in an accomplishment (skip out the door). Children imitated past-imperfective morphology equally well in accomplishments and activities, but they imitated past-perfective morphology with higher accuracy in accomplishments than activities. These findings suggest that children's early morphology development is influenced by lexical aspect conveyed at the sentence level, as predicted by the PROTOTYPE HYPOTHESIS.