During a training course, trainers and trainees develop a joint activity: the activity of each one is determined by the activity of the other participants. This paper is based on detailed analysis of the activity in continuing vocational training, according to an analysis methodology which is that of vocational didactics research field. This paper discuss the observed forms of interaction between participants in the training and learning outcomes that result.

The subjects of this research are professionals who come in training to learn to use a land management software, GIS (Geographical Information System). The research shows that the activity in training doesn't consists on the one hand, for trainers to provide knowledge, ways of doing things, information and rules needed to act effectively and on the other hand, for learners to integrate unequivocally what the trainers and the training situations provide to them.When professionals engage in training, they bring with them in the classroom their whole work experience regarding the subject of training (Pastré, Mayen et Vergnaud, 2006, Pastré, 2008). We can actually see that on arriving in GIS training, learners have representations of the object of the intended learning. They have more or less developed knowledge. They have experimented GIS software, trying to use it independently. They have also the experience of the work tasks they must perform with GIS.

All this knowledge that professionals have acquired by experience emerge during training. People make reference. Sometimes they support learning. At other times they impede learning.

Being present permanently in training, knowledge and experience of trainees affect the activity of trainers. These can be regarded as obstacles to the planned schedule of training and kept away. Trainers may also attempt to exploit the learning potential of the work situations that are familiar to learners (Holgado, 2011) and are for them potential situations of development (Mayen, 2007).

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