In this paper we discuss an imporant aspect of human tutorial dialogue -- the use of acknowledgments -- and present a critique of earlier work on the use of acknowledgments in synthesizing tutorial dialogues for Intelligent Tutoring Systems (Evens et al, 1993). Our goal is to establish a more solid theoretical base for studying and synthesizing tutorial dialogues than what was used in the earlier work. A proposed foundation for this study is the idea of language use as a joint activity composed of joint actions, presented by Clark (1996). It appears to provide a more powerful conceptual linguistic framework within which to describe the behavior of human tutors and shows promise as a guide for synthesizing tutorial dialogues in Intelligent Tutoring Systems. In particular, we are investigating the role of acknowledgments as the mechanism that makes joint action possible. It is our thesis that an acknowledgment is anything that signals closure or lack of closure of a joint action.