Collaborative learning assumes that knowledge is constructed through negotiation and discussion. This exploratory study focuses on 2 groups of 3 pre-service primary teachers solving 2 mathematical tasks in a text-based and asynchronous WorkMates learning environment. This case study describes the group processes, and the different patterns of group interaction are analyzed. The assumption is that the process of socially shared metacognition is especially effective in learning how to solve problems in groups. Socially shared metacognition emerges when a group member regulates a group's problem-solving process and the other group members react to the initiative. Individuals' retrospectively reported feelings of difficulty during the task are taken as a measure to show whether group interactions contribute to individual learning. The results suggest that, when socially shared metacognition emerges, individuals' feelings of difficulty decrease. Important is that individual group members with adequate (meta)cognitive skills take the initiative and other members react upon it. Suggestions for future research are discussed. (Contains 3 tables and 4 figures.)