Our paper presents a cooperative engineering project (Sensevy & Bloor, 2019) exemplifying the cooperative schemes developed within the Didactique pour Enseigner collective (CDpE, 2019). These concrete examples of cooperative projects enable a discussion of epistemological, theoretical and ethical aspects at the core of cooperative engineering. We will present the framework of ACE cooperative engineering (Arithmetic and Comprehension in Elementary School) how a collective of teachers and researchers has been built (Joffredo-Le Brun et al, 2018). This framework highlights the need to suspend judgments by any potential observer of practices, to allow the implementation of a common observation apparatus to support collective work. We will show how this observation device, initially in the form of cards (Quilio & Mercier, 2018) and then in the form of Picture-Text-Audio Hybrid Systems (PTAHS) (Blocher, 2018), builds a common background of experience and a shared means of describing didactic facts (Sensevy et al, 2019). Carried by the idea (Mercier et al., 2001) of a didactic process produced under the double control of users and available theories, this instrument has become indispensable to the cooperative work. It allows to produce cultural evidence (Sensevy, Cariou, Santini and Quilio, 2018), as exemplars (Kuhn, 1990) of didactic facts in the common work. This instrument for observation and documentation enables a common thought on the problems encountered in practice, that teachers and researchers can analyze, each from their own point of view, to progressively share their analysis.

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