Residential adventure education is a surprisingly powerful developmental experience. This paper reports on a mixed-methods study focused on English primary school pupils aged 9-11, which used complexity theory to throw light on the synergistic inter-relationships between the different aspects of that experience. Broadly expressed, the research question was how (if at all) do pupils change following a residential adventure education experience, how does any change relate to their experience during the course and what are the implications? Qualitative findings suggest that the process of personal development through residential adventure education is a complex system, in which transformative step changes arise in some pupils as a natural and possibly inevitable consequence of the complex nature of the process. Quantitative findings include evidence that the number of schools that offer residential experience is increasing but that fewer opportunities are available in schools with more deprived catchment areas. An instrument to assess the impact of a residential experience on pupils was designed and tested, showing four reliable components: living with others, challenge, teacher relationships and learning about self. Pupils' classroom attainment was significantly correlated with their perception of the impact of the course. There was a significant improvement in prosocial behaviour and a significant reduction in self-perceived hyperactivity from pre-course to post-course. (Contains 2 tables and 1 figure.)