The purpose of this paper is to show that data mining tools can help refine the understanding of what happens on a platform of collaborative work. For this, we compare a multimodal analysis of traces with an analysis of these same traces performed by data mining tools. The second analysis confirms the results of the first one on some points but also gives more information and reveals some “dysfunctions” in the use of the platform. So, it seems interesting to use such tools to allow a formative evaluation of the training devices.