The research reported in this paper analyses teaching dilemmas experienced by four in-service teachers in the context of a reform-oriented teaching approach for primary mathematics called Developmental Education in Mathematics (DEM). The findings exemplify three teaching dilemmas: Whether to tell students how to solve a challenging task; what to do when students are bored with an important task; and trying to keep the pace of the lesson while supporting all students in the classroom. Importantly, the origins of these dilemmas were found to lie in internal tensions between the components of the DEM system, which the teachers had implemented. Finally, the implications for development of curricular material, implementation of reform-oriented teaching approaches, and the professional development of teachers are discussed.