This study describes a method of self-assessment for learners in a collaborative discussion. The authors propose a method of self-assessment in an online discussion and examine its effectiveness through the development and evaluation of a software program to visualize the discussion on a Bulletin Board System. The software, referred to as "i-Bee" (Bulletin board Enrollee Envisioner), can visually display the co-occurrence relation between keywords and learners. Thus, the i-Bee can display the content-wise contribution made by each learner to the discussion. In addition, the i-Bee can display the recent level of participation of each learner and the frequency of each keyword used by the learners. The i-Bee enables students to assess and reflect over their discussion, to understand the condition, and to reorganize their commitment in a discussion reflecting their learning activity.