This study explored the collaborative production of mathematical knowledge during computer-mediated learning activities. In particular, it focused on opportunities for undergraduate students from a local university to collaborate with elementary-aged at-risk children on commercially available computer games in an urban after-school club. Two types of qualitative data collection techniques were employed: participant observation notes and videotapes of participants interacting at computers. The study focuses on two participants, a fourth grader and a third-year undergraduate student. Undergraduate participation in the after-school club was found to play a significant role in organizing collaborative activities for children. While many of the strategies for collaboration used by the undergraduates did not necessarily lead to the co-production of mathematical talk or reasoning, that was not the case for explicit requests for explanations. When children had solved a problem, it was common for undergraduates to ask them what they did to accomplish the task; this resulted in the children giving explanations, although they tended to be brief and provide no evidence of deep understanding of mathematics. Results indicate that it is crucial for differences in problems to be systematically explored given that exploration of the mathematical patterns found in solution strategies provides children with opportunities to construct a deep understanding of principles underlying mathematics. (AEF)