Collaborative learning requires the students’ organisation within their small group and a certain level of Collaborative Decision Making (CDM) in the development of their joint activity. Effective CDM requires organisation and consensus building among a group of persons that could have different levels of knowledge and different ways to interact in the context of a group. Reaching a consensus could be affected not only by the knowledge of the group members individually, the quality of the information, but also by the knowledge each of the team-mates’ have about their team-mates’ knowledge and their capacity to collaborate in the CDM. Considering the interest of cognitive tools for helping the students represent what they know and facilitate critical thinking, deep learning and transformation of information into knowledge, we have introduced a group awareness feature aiming to increase the knowledge group awareness between the members of the small group. The group awareness widget displays the students’ level of certainty during their joint activity in a finance activity developed as a Serious Game. We analyze the effects of the group awareness widget in the CDM process and the effect on the performance of the group.