A study was undertaken to determine how much knowledge children have of grammatical systems before they evidence the systems in their spontaneous speech in a productive way. A child aged about two and a half years was examined over several months through elicited imitation causing him to repeat a model sentence immediately after the researcher. Three kinds of sentences with modal auxiliaries were used--affirmative declarative sentences, affirmative yes-no questions and affirmative wh- questions--at two periods prior to the child's actual use of these forms. Grammatical and ungrammatical sentences were presented in each category. Correct imitations and efforts to restructure and normalize the sentences showed the child had a fair amount of knowledge of the distributional characteristics of auxiliaries in declarative sentences but little command over those in questions. Results suggest extensive pre-analysis of the auxiliary systems, keeping pace with but preceding spontaneous use of the grammatical forms. (CK)