The spontaneous verbal interactions of two children and their babysitter were recorded over the period of half a year. The children were males from middle-class backgrounds and two years old at the beginning of the observation period. Imitated utterances were found to surpass quantitatively spontaneous ones on the

dimensions of grammatical and semantic complexity. With few exceptions, new structures appeared first in imitative utterances and only later in spontaneous ones. Both the higher complexity and the prior appearance of new constructions in imitative utterances suggest that imitation fulfilled a progressive function for the observed children.