This study explores the use of ‘retrodictive qualitative modelling’ (RQM), a novel approach described for L2 research by Dörnyei (2014) that involves the identification of learner archetypes and motivational patterns in empirical research. The method reverses the traditional way of conducting research; it first examines the outcome – that is, the end-states – and then traces back the developmental trajectories leading to this outcome. Situated in a Hong Kong secondary school, we started our project by first asking a teacher focus group to identify salient learner archetypes in their classrooms (Years 7 to 9), and on the basis of these we then conducted in-depth interviews with one prototypical learner from each group. As a result, we gained insights into the ‘signature dynamics’ of the motivational system associated with each prototype. Our focus in this chapter is on evaluating RQM in action. First we report on the processes in which teachers identified learner archetypes and thereafter offer an in-depth analysis of the system dynamics of one of these students. In the final discussion, we list the main methodological lessons that we have learnt from applying RQM.