This contribution tells an experience of vocational training in the certificative evaluation of oral skills in French as a foreign language. First, it approaches the plasticity of the interaction on these situations of face-to-face evaluation and of the interdependence between interaction and assessment. Secondly, it focuses on the ways students mobilize these analysis in the last phase of training, the debriefing, realized after a simulation of examination. This phase allows the novice professionals to estimate their modes of participation and to identify the contextual components of the situation. Finally, the gains of the analysis of the interactions to design the devices of training are discussed.