This study investigates the impact of a sail training education programme on the self-concept of a group of 147 adolescents. The Competence and Social domains of Bracken's self-concept scale were assessed by a quasi-experimental design in three phases: before commencement of the activities, on the last day of the voyage, and three months after completion of the programme. A significant difference (Competence: effect size 0.2, p less than 0.001; Social: effect size 0.23, p less than 0.05) was identified soon after the sail experience, but this effect was only temporary. Our analysis was confirmed by a bootstrapping technique. Bronfenbrenner's bio-ecological theory was used as a general interpretative framework in order to identify personal and environmental factors that can sustain developmental changes over time. (Contains 4 tables.)