What is the practical pedagogic value of the zone of proximal development? How might we draw from the writings of Vygotsky and Leont'ev with regard to understanding the process of children and young people's development as socialised intellectual beings? This article applies cultural-historical theory to classroom activity in order to reveal the potential for dynamic change in subjectivity, agency, cooperation and collaboration. After a detailed theoretical contextualisation which links primary sources and the cultural-historical tradition to learning and development through classroom activity, an incident in a lesson is discussed and situated in its wider narrative of practical experimentation, diagnosis and implementation.