We are developing a set of handheld input devices for mutual assessment in the course of a learning activity and a system to give on-the-spot feedback concerning the summary of the assessment to the learners visually with the aid of charts. This paper describes its design concept and provides an overview of the system. Keywords Mutual assessment, collaborative learning, social constructivism, educational assessment, ethnomethodology ACM Classification Keywords K3.1 [Computers and Education]: Computer Uses in Education, H.5.3 [Information Interfaces and Presentation]: Group and Organization Interface