This project aims at developing observational and quasi-experimental studies to explore how argumentation emerges as a context-bounded activity in children who are invited to reach a joint decision or solve a common task in an ad hoc designed setting. It takes place at the crossroads of different lines of research: a neo-piagetian and neo-vygotskian concern for the socio-cognitive development of higher psychological processes; a socio-cultural approach of participative interactions within goal-directed activities; and the recent advances of argumentation theories. It seems the proper moment to revisit these classical studies, as well as the post-piagetian studies of conservation in conversation, with the possibility, now available, to reconsider the argumentation in children's talk beyond Piaget's own reductionistic logicism on these matters. The main goal of the project is to contribute to the understanding of the psychosocial processes that are involved in argumentation. We will concentrate on 4- to 7-years- old children, using tasks inspired by the piagetian tradition, that have already been widely studied in the literature (mainly conservations tasks, perhaps others). The project will imply two different contexts: the laboratory, in which we will concentrate on the observation of argumentative activities organized by the researcher in controlled settings in order to contribute to quasi-experimental research; and the classroom, in which we will design activities in collaboration with the teacher. Special attention will be paid to the implicit rules that structure the life of a classroom in order to examine to which extend they sustain socio-cognitive interactions such as argumentation.