It is believed that computer-supported collaboration at a distance can stimulate learning. In this paper an innovative environment that permits real-time collaborative problem solving is described. In particular we study the effect of two alternative coordination mechanisms on the problem solving activity of pairs of students engaged in concept map building. The first mechanism imposes locking of the shared activity board for one student at a time, while the second mechanism allows access of all group members to the shared activity board in a contemporary way. The reported findings are of interest to researchers and practitioners who are involved in the design and study of real-time collaborative learning environments.