This paper presents an experimental research that focuses on collaboration in a multi-player game. The aim of the project is to study the cognitive impacts of awareness tools, i.e. artifacts that allow users of a collaborative system to be aware of what is going on in the joint virtual environment. The focus is on finding an effect on performance as well as on the representation an individual builds of what his partner knows, plans and intends to do (i.e. mutual modeling). We find that using awareness tools has a significant effect by improving task performance. However, the players who were provided with this tool did not show any improvement of their mutual modeling. Further analysis on contrasted groups revealed that there was an effect of the awareness tool on mutual modeling for players who spent a large amount of time using the tool.