There is a need for collaborative group activities that promote student social interaction in the classroom. Handheld computers interconnected by a wireless network allow people who work on a common task to interact face to face while maintaining the mediation afforded by a technology-based system. Wirelessly interconnected handhelds open up new opportunities for introducing collaboration and thereby changing classroom pedagogical practices. We present a conceptual framework and a method for the design of a mobile computer-supported collaborative learning system based on Activity Theory. An instance of the framework for teaching basic mathematics skills was evaluated with 24 6- and 7-year-old children in a month-long study. Positive effects were observed on student social interaction, motivation and learning.