This study examines whether the assumptions of the Transtheoretical Model (TTM) are useful to evaluate the effectiveness of a school-based stress prevention programme in adolescence to promote appropriate coping behaviour. The TTM assumes three consecutive phases in the adoption of behavioural patterns. Progress throughout the phases is promoted by three developmental determinants. It, therefore, was expected that programme participation is associated with a progression throughout the phases and with a change in the developmental determinants. Of 372 adolescents, aged between 13 and 16 years, 190 participated in a control condition and 182 in a stress prevention programme. Measurements were taken a week before (pre-test), a week after (post-test) and 12 weeks after the training (follow-up-test). Results indicated that adolescents in different phases of behaviour change report different numbers of stress symptoms. Programme participation is associated with a progression in phases which, however, was not stable after the programme had run its course. Besides this, adolescents in different phases benefit from participation differentially as different patterns of changes in the developmental determinants show. A systematic promotion in the different phases of behavioural change by integrating TTM-tailored "tools" into a stress management programme may improve participants' intention and competence to actually show appropriate coping behaviour. (Contains 4 figures and 2 tables.)