This thesis describes research in a small, but significant, area of human-computer-interaction (HCI) through natural language. It deals with the problem of how humans and
computers can coordinate their communication through the use of acknowledgments and related phenomena. My primary goals are 1) to advance the understanding of coordination
in communication by drawing together information about how coordination is understood in a number of different fields, 2) to describe coordination in tutorial dialogue, and 3) to
propose a model of how intelligent tutoring systems (ITSs) should generate acknowledgments in language.