Development, as Vygotski (1978) suggested, is the process by which a person transforms himself/herself through an activity, in a socio-techno-cultural context. According to this socio-constructivist psychologist, learning is prior to development. Indeed, this approach considers that development occurs during and through activities, and is not linked to "developmental stages" of an individual person. As theorists of enaction, Maturana and Varela (1987) argued that cognition is a concrete action, and that every action is cognition. We agree with this assumption. We adopt an externalist approach to cognition, from situated and distributed cognition theories (Suchman, 1987; Hutchins, 1995, 2005). According to this externalist approach to cognition, we state that observing cognition as a dynamic process is not simple. We also think that development must be "in motion" to be studied, that is, to be in the very act of emerging from interactions between the user and the system. But activity cannot be directly observed and studied. Though, activity traces can provide information about the core of activity. To conduct such analyses, we use an ethnomethodological method in our research. We can formulate two specific questions for this work. First, we suppose that observing both the use of visible interaction traces in a collaborative activity and the appropriation of the technical environment will lead us to better understand the possible role of visible traces in human-computer interactions. Second, we hope that watching attentively to the activity distribution between humans and non-humans (Latour, 1989) and to the position of the use of experience via traces will point out the situated, distributed and opportunist natures of activity we study. Concrete situation… We study the activity of two distant mediated learners who use a computer and work by peer. They design operating instructions for a procedural task, an origami paper-folding. Instructions they have to co-write must allow someone to realize the origami. For that activity, they make use of a computer offering a three areas interface, proposing: a personal video showing action of real hands folding a sheet of paper, and two shared areas: a chat and a text editor. Instructions have to be designed in the text editor. The two shared areas afford traces of what has been done, providing for the co-writers immediate footprints of activity. With this testing, the first goal is to observe the activity of mediated distant co-writing taking place and the possible self-regulation induced by experience traces from shared areas. More widely, we also want to be present at how the cognition is distributed through the different areas of the interface for this particular task. All subjects' actions on computer are recorded: chat interactions, edited text, video plays. We have transcribed interactions, between co-writers, occurring in discursive areas of the environment. A piece of transcription is illustrated below. temps chat privé Rastaban chat publié chat privé Yildun éditeur de textes