We use a combination of network analysis (NA), text-mining (TM) techniques, and thematic discourse analysis (TDA) to characterise and compare student discussions about sustainable development. Three student groups at three different times were analysed. The analysis entails an iterative design where NA, TM, and TDA continuously inform each other to produce a rich and coherent picture of the discussions. The output of such an analysis is a set of maps of these discussions, which have both qualitative and quantitative uses. Qualitatively, the maps show how thematic patterns in the discussions are related for each group, and we see developments in student discourse with each discussion. Quantitatively, we use network motif analysis, entropy based measures, and degree distributions to distinguish between discussions.