Ideas of categorisation and pattern have been used in the past research of all three authors; on teachers’ complex decision-making (Brown and Coles, 2000) and students’ reasoning in mathematics classrooms (Reid, 1999, 2002). We illustrate these ideas with an analysis of two transcripts. As we reflect on how categories are formed it becomes clear that decision-making in the complex world of classrooms often takes place without time for reflection. Damasio (1996) develops what he calls his ‘somatic marker hypothesis’ to account for how people manage such decisionmaking. By ‘somatic marker’ Damasio means a bodily predisposition that informs decision-making. We then provide a second analysis of the two transcripts, illustrating how we currently observe the development of somatic markers through the language used and decisions made in classrooms.