Case studies have been constructed of primary school children's developing explanations of a range of air pressure phenomena. A range of conceptions relating to air pressure have been identified, and insights gained concerning the way these interrelate over time and over context. It was found that children are naturally generative in their construction of explanations, but that they use conceptions in quite complex and fluid ways. It is argued that naive conceptions maintain a valuable function as intuitive recognition elements that feed more sophisticated conceptions, and that generating a satisfying explanation for a phenomenon can involve having access to a range of interrelated conceptions. A range of contextual factors were identified, which influence the construction of explanations, and can act as barriers to the application of scientific conceptions.