This paper aims to analyse if virtual forums set up in an environment specifically designed to improve collaborative learning can effectively influence students' discourse quality and learning when compared with those forums set up in a general environment. Following a coding schema based upon the set of scaffolds offered in the Knowledge Forum environment, we have qualitatively analysed 60 forums and 1370 students from different subjects. The results show that there are very few elaborated and shared deep discussions: the central axis in those superior contributions focuses on bringing new information to already written contributions. There are more new and contrasting opinions in forums set up in a specific virtual environment, whereas there is more reasoning and elaboration in those that were set up in a general one. We propose some explanations for this dissonance and we conclude that collaborative virtual environments are secondary aspects in accounting for deep exchanges of information. Therefore, there are many aspects that need to be taken into account to improve collaborative learning and knowledge building.