Debating in educational situations can enable students to gain deeper understanding of the views that are being discussed, to acquire new arguments and ideas, and to form more reasonable personal opinions. However, analysing such subtle forms of interactive knowledge restructuring remains a problem for collaborative learning research. In this paper we present a framework for analysing how and when students broaden and deepen their understanding of a space of debate. The framework is termed “Rainbow” since it comprises seven principal analytical categories, to each of which a colour is assigned, thus enabling data-visualisation in marked-up interaction corpora. The categories distinguish between activities that are part of the prescribed assignment and activities that are not, and between task-focussed and non task-focussed activities. Activities focussed on maintaining the interaction itself are distinguished from argumentative interaction. Notably, an operational definition of what it means to broaden and deepen understanding in this case is also provided here. The functional Rainbow analysis is complemented by an analysis of topics and subtopics that enables identification of one form of conceptual deepening of the question. We propose that the Rainbow framework satisfies criteria of simplicity, coherence and coverage as an analytical method, which makes it suitable for extension to other educational situations. Possible extensions to the framework are discussed, with respect to additional CSCL tools, domains and tasks.