This study explores the effectiveness of a cooperative learning (CL) approach, where students work together and elaborate concepts of physics. The group problem-solving tasks were conceptual questions from physics, where the students had to discuss and provide explanations of some phenomena. The effectiveness of the learning-in-groups approach was validated and correlated with working group interactiveness. Two group variables were assigned: the group performance and the group activity. These variables and the subjects' participation variable were correlated with achievement. Discourse analysis revealed variation in the nature of the interactions and information exchange, and the two roles as learners and learning facilitators. In addition, the study provided evidence for some features of cooperative learning that could characterize it as a nonlinear dynamical process. Implications of the findings are discussed.