ICT tools have been developed to facilitate web-based learning through and learning about argumentation. In this paper we will present an example of a learning activity mediated by Digalo--software for knowledge sharing through visually supported discussion--developed in a university setting. Our aim is to examine, in particular, socio-cognitive construction of knowledge and argumentation by students debating a controversial question in history. We propose a descriptive approach of understanding and meaning-making processes based on two levels of analysis: (1) a topic meaning-making process oriented level and (2) an argumentation oriented level. We focus our studies on how the participants--small groups of students--develop understanding of the topic, their arguments and their interactions through the use of different functionalities of this software. Our results show that interactive and argumentative processes are themselves objects of learning and develop through collective activity. Development of the understanding of the topic through argumentation is discussed and linked to the design of the activity and the affordances of the Digalo software.