The relation between age and mean length of utterance in morphemes (MLU) was evaluated in a sample of 48 preschool children between 24 and 50 months of age. Twenty-four of these children were diagnosed as having a specific language impairment, and 24 were considered language normal. The groups were matched on age, race, sex, and parental education level. A majority of the children in each group were from lower-middle-class backgrounds. MLU was derived from 20-min mother-child conversations as the dyad engaged in free play. The results showed that (a) age and MLU were significantly correlated in the normal group (r = .75) and in the group of specifically language-impaired children (r = .77), (b) the predicted MLU of the language-impaired group was lower than that of the normal group across the age range, and (c) the rate of MLU change in each group was similar. The age-MLU relation observed in the lower-middle-class normal children compared favorably to that reported previously for middle- to upper-middle-class children (Miller & Chapman, 1981). The finding that MLU changed at a similar rate in the normal and language-impaired groups is evaluated in light of the observation that childhood language disability is usually associated with slower rates of language development.