The aims of this study were to examine whether pupils attending a programme at a residential outdoor education centre experienced an increase in psychological wellbeing and to explore the underlying mechanisms behind any increase. This was achieved through the use of a mixed methods framework, based on a Realistic Evaluation approach (Pawson and Tilley, 1997). Realist Synthesis was carried out to derive tentative programme theories from the extant literature. These tentative programme theories were then tested based on data collected from focus groups with pupils and residential centre staff, interviews with school staff, pre- and post- intervention measures of pupil psychological wellbeing, and observations, recorded as field notes during the residential. The results suggested that pupils experienced a small, but non-significant increase in psychological wellbeing. Four final programme theories were developed, concerning Risk and Challenge, The Natural Environment, The Supportive Community and Independence. Limitations of the research are discussed, along with directions for future research. Implications for the role of the educational psychologist are highlighted.