This article aims to unravel a mature student's processes of social engagement at a university, based on nine years of biographical interview data. By framing itself within the realist social theory, this paper analytically distinguishes between precedent social conditioning factors, social engagement processes, and their consequences of learning outcomes in a temporal perspective. In this way, this study attempts to explain how the mature student came to activate or inactivate agency in interaction with changing social circumstances at the university over time. The results of the study show that mediatory mechanisms between social structure and learner agency are the mature student's mobilisation of diverse modes of personal reflexivity and her development of relational reflexivity. The empirical evidence reconciles the competing theorisation of reflexivity between durable disposition and temporary strategy, indicating what matters in student learning from the mature student's viewpoint are changing relational and reflexive dynamics throughout time.