Our work concerns the joint work of a primary school teacher, her students and a scientific mediator, during the visit of an temporary exhibition of a scientific theme in France. Our study aims at analysing and describing the interactions between these different agents and to link them with the resources used in the observed situations: animations about planets in the solar system, bones and articulations, underground water and sand.

We used two different theoretical frameworks in didactics: joint action, and documentation/resources. The theory of joint action in didactics (Gruson, Forest, & Loquet, 2012; Santini, 2013; Sensevy, 2012, 2014; Sensevy, Forest, Quilio, & Morales, 2013; Tiberghien, Malkoun, Buty, Souassy, & Mortimer, 2007) permits to describe and interpret the didactical situations we observe, the teaching-learning process taking into account the knowledge involved, the didactic contract between the mediator and his public, the milieu (Brousseau, 1998) organised by the mediator.

The didactic contract (Brousseau, 1997) is viewed as a system of mutual expectations. It comprises of an explicit part presented in the situation, and of an implicit part corresponding to habits shared by the teacher and the students. In the Joint Action Theory, the contract is seen as a system of knowledge already present, that the students draws on to tackle the new situation.

In the case we study: the first encounter between a scientifc mediator and his public in the science exhibition, we consider that the contract comprises the knowledge likely to be expected from the agents.

The milieu is the set of all symbolic and material elements organised by the mediator, that the public must combine to develop knowledge.

The milieu semiosis is the process of interpretation of the milieu. The Joint Action Theory conceives the didactical situation like a joint action between the mediator and his public. We consider that the agents intend to produce signs for others, and to decipher signs, but that they also inconsciously produce and decipher signs. With this perspective, the students who shows a given relation to knowledge in his/her productions constructs a sign for the teacher. This is the semiosis process, from students addressed to the teacher; but a reverse process from teacher to students naturally also exists. We consider that the didactical situation comprises of a sequence of knowledge games between the mediator and his public.

One of the motivations driving the visitors of the exhibition consists in the resources potential that the publis can meet there, in particular the authentic objects present, as usually in scientific exhibitions (Falk & Dierking, 2000, p. 139).

More generally, alike Adler (2000) we define resources as anything likely to re-source a professional practice; we extend this definition to anything likely to resource one's knowledge. For the agents of the situations studied, the resources permit to build knowledge for teaching or for learning. We observe a resource system (Gueudet, Pepin, & Trouche, 2012) with resources organised and connected by the joint action of the mediator and of his public.

In the situations we study, the mediators present scientific knowledge and use for this aim semiotic resources as described by researchers on communication (Pozzer-Ardenghi & Roth, 2009). These situations are germane to classroom situations, where the teacher uses proxemic resources: the direction of his/her own body and look, the space between him/her and the students, the touch (Forest, 2008).

In this co-intervention situation, which are the roles of each agent? What is the nature of this joint work? Which factors influence it? How can scientific authenticity of resources be defined, within this didactic situation?

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