In any successful conversation, a speaker must select both what is said and how it is said on the basis of various estimates of the listener's abilities, knowledge and interests. Most research on linguistic input to children has focused on the tendency of speakers to simplify their speech for the younger listener. Little attention has been paid to the ways in which adults might introduce material that is outside the child's current system, but that the child is ready to acquire. This paper reports a longitudinal study of the "fine-tuning" of parents' speech to a child over a particular conceptual domain: reference to events that happened outside the current context at an earlier point in time. Reference to past in the adults' speech was chosen for study since temporal reference is a complex part of language acquisition where one finds both the child's comprehension and usage changing gradually over a long period of time. The data consisted of transcripts of interactions between a first-born child and her mother or father when she was 20 months to 29 months old. It was concluded that speakers are sensitive to specific cues from the linguistic behavior of the child, and use these cues in selecting topics that (1) structure the conversation to allow the child to participate most effectively, and (2) present opportunities for the child to acquire new forms at appropriate times. (Author/AMH)