For a large part of its history cognitive science has been grounded in views of the mind based on the traditional Cartesian dualisms. These dichotomies have been reinforced in particular by the view of the mind as an encased symbol-processing system ''protected from the external world'' (Newell, A., Rosenbloom, P. S., & Laird J. E. (1990). Symbolic architectures for cognition. In M. I. Posner (Ed.), Foundations of cognitive science, Cambridge, MA: Bradford Books/MIT Press, pp. 93-131: 107). Cultural-Historical Activity Theory (CHAT) seeks to supersede Cartesianism, thinking about cognition and culture as mutually constitutive of each other. This approach analyzes thought processes as embedded in and manifested through systems of historically developing, culturally mediated activity. Consequently for CHAT, a basic unit for the study of human thought is joint mediated activity. In this paper we will discuss an example of research that follows the CHAT approach to the analysis of learning and development. The data sample is taken from a session of the Fifth Dimension, an after-school activity designed to implement CHAT principles in order to promote the cognitive and social development of adult and child participants alike. (C) 2007 Elsevier B.V. All rights reserved.