Examines the effect of group size on students' behavior in asynchronous, nonmandatory instructional discussion groups. Focuses on four main questions on whether group size: affects the proportion of learner-learner and instructor-learner interactions; influences number of messages instructors post; have an effect on number of contributions that students post; and affect instructor lag time as well as the interval between successive postings. Findings revealed that group size affects all aspects. (Author/AEF)