This study examined the effect of lexical aspect and phonology on regular past-tense production. Data are presented from a group of 31 children, mean age 33 months, with typical language development. A case study of a 50-month-old child with Specific Language Impairment (SLI) is also presented. Children imitated sentence pairs that included an endpoint (accomplishments, e.g. she crawled into a box) or did not (activity, e.g. she crawled around in circles). Verbs ended in obstruents (e.g. walk) or nonobstruents (e.g. roll). The regular past tense was produced with the lowest accuracy in activities ending in obstruents (e.g., she walked in circles). Assessment and treatment suggestions for children with SLI are provided. (Contains 6 tables.)