To find out what factors are involved in a child's learning of syntax, investigators studied the syntactic complexity of the language a mother and child use when talking to each other. The complexity measure used was one developed by Dr. Sheldon Frank and Dr. Harry Osser, and is based on the concepts of generative grammar and transformations. Language samples were collected from mothers alone in an interview and mothers and children together in a play session. There were two groups of mother-child pairs: one from Harlem (black lower class) and one from Washington Square (white middle class). Analysis of the language samples indicated that all the mothers greatly reduced their syntactic complexity when talking to their children, but each mother's language was still more complex than that of her child. There was no difference between the Harlem mothers and the Washington Square mothers in their syntactic complexity in the interview, but the Harlem mother-child interactions were less complex and more didactic than those of the Washington Square group. Finally, the Harlem children seemed to articulate less clearly than the Washington Square children and their mothers had more difficulty in understanding them. There were more requests for clarification in the Harlem interactions. (MH)