This paper deals with a design of a CSCL (Computer Supported Collaborative Learning), referred to as "ProjectBoard", which displays an awareness of task status and division of labor in Project-based Learning (PBL). According to the situated learning theory, learners learn not only the cultural practice but also the "legitimate learning strategy," which refers to the way in which learners can learn effectively in the community using their meta cognition. Based on this concept, learners are expected to monitor the actual status of their achievement by themselves in order to improve their learning in PBL. The authors designed a CSCL which supports learners in the self assessment of their PBL. "ProjectBoard" was developed to enhance learners' reorganization of their learning activity based on the awareness of the status of their collaboration. Through its implementation in an undergraduate course, the learners evaluated the effectiveness of ProjectBoard in monitoring their learning activity.