This phase was planned to comprise 180 min of time in the classroom with the students and their teacher. Because of interruption of the study (see below), it finally only lasted 125 min of classroom time. During this phase, students were supposed to work in six groups of four. However, log-file analysis showed that in each chat room, there were between 7 and 12 logged-on participants (10 on average). There were seven ‘nomadic’ participants who each logged on to at least four of the six chat rooms, with either humoristic pseudonyms (e.g. ‘the click in the shadows’), random characters (e.g. ‘??????????’), or else recognizable ini- tials and names. In each chat room, only one or two stu- dents out of the four actually created the argument diagram. In two groups’ chat rooms, the diagram was deleted just before the end of the session, in whole or in part.