The paper presents a specific case of how interdisciplinary approach to teaching elementary mathematics can be conceived. In this context, the mathematical concept of circle is delivered through physical education environment, during a lesson aimed at speed training. The rationale for this approach is that a teacher at the primary stage in Slovakia usually teaches all subjects in a grade and can thus integrate their curricula. The basic pedagogical premises in this study are constructivism (Bruner, 1996; Dienes, 1971; Piaget, 1973) and the theory of didactical situations (Brousseau, 2002). The adopted interdisciplinary approach to elementary mathematics education is based on the model of educational reconstruction (Jelemenská et al., 2003) with a specific focus on designing a learning environment. For this purpose, the design-based research methodology was chosen as it provides for both developing relevant educational materials and conducting subsequent research. A three-phase activity was designed to guide the pupils to reflect on the concept of circle. Subsequent intervention was carried out in a physical education lesson with two classes of fourth-graders. As the design-based research methodology focuses on the causality of designed interventions (Nathan, Kim, 2009), the data were collected by the methods of participant observation and individual interview. The analysis of the obtained data indicates that proposed physical activity is potentially effective for learning the concept of circle by primary school pupils.