Little attention has yet been focused on the social nature of metacognition and motivation in adult- or peer-mediated learning, although reciprocal or transactive interaction between individuals is emphasized as a road to learning, that is, in teaching and mediation of knowledge and skills. The present article presents a case analysis and focuses on (a) exploring if and how socially shared-regulation and (b) motivation and coping are manifested in high-ability, 4th grade students’ peer-mediated learning in a technology-based game environment, specifically constructed to foster problem solving in mathematics. The case analysis supported the notion that peer-mediated learning can produce high-level learning and, also, transfer of learning. The key conditions for effective collaboration, task-orientation, and social and cognitive competencies, were met in the case of the peers. The analysis further suggested that the notion of shared-regulation could be helpful in understanding of multilevel interaction and regulatory activities in learning. The concept of shared-regulation best seemed to mirror egalitarian, complementary monitoring and regulation over the task, thus bringing the research closer to phenomena relevant to joint, peer-mediated learning. It seemed that regulation in true collaboration fluctuates among the three modes of regulation, self-, other-, and shared-regulation. We concluded, however, that collaborating peers do not regularly meet these ideal conditions, and that the more complete picture of joint problem solving and regulation is complex and variable. Understanding of these multilevel regulatory activities in learning, and their relationship to other, multilevel concepts like motivation, social competence, context, and learning, is a challenge for future research.