This study explored the differences among online elementary school student groups based on their communication features. Two hundred and ninety-one Taiwanese students, ranging in age from 11 to 12 years old, participated in this study. The students were randomly arranged within-class into three-member groups. Each group was asked to use a collaborative learning system to accomplish a group task generating a shared concept map. The textual discussions in each group during collaboration were collected, coded, categorized, and quantified to profile their communication characteristics. Cluster analysis on the resulting communication characteristics resulted in four types of small student groups, including "passive or reticent," "frequently off-task," "actively participating," and "knowledge emphasizing." Most student groups (56%) were found to be relatively "passive or reticent." "Frequently off-task" student groups made a protrusive amount of messages for off-task social purposes. The "actively participating" student groups were characterized by abundant discussion, particularly for continuing task, managing procedure and coordinating efforts. The distinctive feature of "knowledge emphasizing" student groups was that they devoted particular attention to task related knowledge. In addition, they performed better in task accomplishment. (Contains 2 figures and 3 tables.)