In this paper we propose a novel approach that identifies meaningful student groups more objectively. As the data for objective analysis, we use
communication history records
that are collected from various communication tools such as telephones, e-mails, and messengers. We use the simple intuition that communication history records implicitly contain peer relationship information. We first formally define the notion of
degree of familiarity
between students and present mathematical formulas that compute the degree based on the history records. We then adopt a clustering technique to mine meaningful groups. To use the clustering technique, we define the measure of
between friends based on the degree of familiarity, and perform clustering using the measure. To show the practicality of the proposed method, we have implemented it and interpreted the meaning of experimental results.