Argument visualisation refers to graphical or other non-verbal means of making reasoning chains and conclusions explicit. Constructing argument diagrams is one way to visualise argumentation. The solving of ill-structured problems, commonly related to societal and educational questions, can be facilitated by a visual depiction of the variety of viewpoints relevant to the problem in hand, and the arguments used to support different solutions. In this study 7 male and 10 female Finnish secondary school students were set the task of constructing and elaborating an argument diagram on the issue of genetically modified organisms (GMO). The task proceeded in three successive phases using a network-based tool. The students constructed their first diagram on the basis of their previous knowledge on GMO, modified it after having read three articles on the theme, and finalised the diagram after they had engaged in a dyadic chat debate on the same theme. The diagrams were analysed for shape and ...