Background: Environmental issues are frequently controversial and involve conflicting interests and values. Much environmental education literature explicitly encourages teachers to promote pro-environmental attitudes and behaviours amongst their students, despite evidence that teacher support for such a policy is ambiguous at best. The literature on teaching controversial issues provides conflicting advice for teachers, though many authors advocate the adoption of a neutral or balanced approach. However, there has to date been little research into the strategies which teachers actually adopt in teaching about controversial environmental issues. Purpose: This research aimed to address the gap in the literature by investigating the beliefs and practices of three experienced geography teachers teaching controversial environmental issues in English secondary schools. The study draws upon both interview data and transcripts of classroom interaction. Sample: Three experienced teachers delivering an A-level geography course (Schools Council 16-19) were selected and studied, along with a specific group of their students (aged between 16 and 18 years). A non-interventionist approach was preferred; therefore it was necessary to find classrooms where controversial environmental issues were already being taught. This particular geography course was selected primarily because of its strong focus on environmental topics, and experienced teachers were selected in order to provide a richer depth of practice to draw on. Design and methods: The research utilized a multi-site, instrumental case-study approach, involving the study of three different cases, each illustrating the research focus (of teaching controversial environmental issues) in a different school. The three cases were studied sequentially over the course of two years, and involved spending a total of 5-6 weeks at each site. Within each case study, a series of lessons was observed and semi-structured interviews carried with teachers and selected students from each class. The lessons were recorded on audio tape using a lapel radio-microphone worn by the teacher. Results: In line with much of the literature, the findings reveal that these teachers believed they should adopt a "neutral" or "balanced" approach to teaching controversial environmental issues. However, in the reality of the classroom, such an approach proved unsustainable and the teachers experienced significant difficulties in enacting their beliefs. A detailed analysis of classroom interactions demonstrates that the influence of their own attitudes was greater than they either intended or, in all probability, realized. Conclusions: The analysis suggests that teachers have to choose between explicitly or implicitly expressing their attitudes (through questioning or by control of students' turns in discussion). The study also demonstrates how--through looking in detail at classroom interactions--it is possible to make visible this aspect of the "hidden curriculum." (Contains 1 table.)