This article aims to describe a new tool, the association tool, to collect data of students- discussions on scientific concepts. We have tested the association tool in two different situations. In the first, the association tool was used by student teachers in group-work. The students (two groups, which con- sisted of two and three students respectively) were asked to associate ATP (adenosine triphosphate), a concept with which they are familiar, with other concepts. In the second situation, the association tool was used in an interview situation dealing with the concepts of energy and heat. Three student teachers were interviewed. Both situations were videotaped and the transcripts were analysed quali- tatively and quantitatively to show different ways of using the association tool. The association tool yielded rich data on the discussions of the concepts useinteractions in group-work and an interview situation.