Anthropological approaches to studying the contextual specificity of mathematical thought and practice in schools can productively inform descriptions and analyses of mathematical practices within and across different teaching and learning contexts. In this paper I argue for an anthropological methodological orientation that takes into consideration the proposition that human beings possess biologically endowed, human-specific modes of cognition that have structuring effects on pedagogic practices. I illustrate that aspect of my methodological focus by exploring a case of the use of aggregates in a Grade 3 lesson, arguing that the teacher thinks of aggregates in part-whole terms, as fusions, and not in set-theoretic terms, colouring her evaluations of learners' productions. I use the analysis as an illustration to support my argument that anthropological descriptions of pedagogic practices that emerge in school lessons are enhanced by incorporating accounts of the more general human-specific cognition.