Over the past several years, scholars of teaching and learning have demonstrated the potential of collaborative learning strategies for improving student learning. This paper examines the use of computer-mediated communication to promote collaborative student learning in large introductory sociology courses. Specifically, we summarize a project we conducted during the 2000-2001 academic year in which we added online collaborative learning activities to the curriculum of two large sections of introductory sociology. Drawing on Novak et al.'s (1999) Just-In-Time Teaching methods, we developed online activities to help prepare students for subsequent in-class work and to cultivate a sense of group solidarity among smaller teams within the larger class. The results suggest that student engagement in the online group learning activities was strongly predictive of better student academic achievement on the biweekly quizzes, cumulative final exam, and course paper. These findings highlight the potential value of online group work for fostering collaborative learning environments in large lecture courses as well as for enhancing student learning. (Contains 2 tables.)