Enquiry teaching approaches are widely considered as more useful than didactic approaches for the development of environmentally responsible behaviour. This paper is a report of an empirical study on the validity of this belief with reference to higher-ability and lower- to medium-ability groups drawn from geography classes at the Advanced Level in Hong Kong. The hypotheses were that, taken together, enquiry approaches are more effective than didactic approaches for the development of environmentally responsible behaviour in both the short and long terms for students as a whole, and for students within the same range of academic ability. A quasi-experimental control group design was used for selecting students and classes from schools in the territory. A questionnaire survey and a series of interviews were conducted to collect data about students' behaviour before and after they were taught a people-environment topic with a didactic approach or an enquiry approach. The results suggest that the students on the whole were not behaving as positively for the environment as their peers in other countries. For both the higher- and the lower- to medium-ability classes, those who were taught with an enquiry approach were behaving positively in more areas than those who were taught with a didactic approach in both the short and long terms. This trend could be attributed to their greater attention to critical thinking, positive behavioural changes, and the development of internal locus of control, while society as a whole was still largely apathetic to personal efforts for improving environmental quality. To further enhance the effectiveness of enquiry for the development of environmentally responsible behaviour, it is suggested that teachers should give more attention to the elements of concern and empathy in the classroom. Improvements in teacher education and training and in the guidelines for teachers, restructuring and revision of environmental education in schools, providing