Inquiry-based learning (IBL) has become a common theme in both school and higher education in recent years. It suggests a model of curriculum development and practice that moves educational debate beyond teacher or student-based approaches towards a model of teaching and learning in which the endeavour is shared. This paper discusses an investigation into the practice of IBL among primary schoolchildren in the setting of the Primary Years Programme of the International Baccalaureate. Three ideas from the work of the philosopher C.S. Peirce are used to provide an epistemological base for analysing the pedagogical practice of IBL: semiotics, reasoning and community of inquiry. Findings are presented under these three headings to illustrate the potency of Peirce's conceptualisation of learning. Drawing in particular on findings from a unit of inquiry on maps and mapping, it suggests an empirical frame for IBL for the use of teachers in the development and assessment of IBL.