Citizenship educators have not yet developed a satisfactory framework for describing the conceptual knowledge at the heart of their subject and the complex ways in which students develop understanding. By focusing on how young people (10-18 years of age) use the core citizenship concepts of power and agency, this research provides an insight into how students learn. Our analysis of young people's work reveals that many of them are operating with a pre-political or politically naïve understanding of the world which limits their ability to understand power and agency. Some students have gone on to develop a greater sense of their own agency within complex chains of influence, which demonstrates a more nuanced understanding of power and agency, rooted in a more political reading of world. We conclude that our findings may help citizenship teachers to plan more consciously to tackle this area of conceptual understanding.