The conservation of biodiversity is an important socio-scientific issue that is often regarded as a precondition to sustainable development. The foundation for citizens' understanding of conservation issues can be laid down in formal school education. This research focuses on decision-making discussions about biological conservation issues among 131 15-16-year-old students, to address two main research questions: (1) Can peer group decision-making discussions, in a normal science lesson setting, help develop students' personal reasoning in relation to conservation issues?; and (2) Are there features common to high quality discussions about conservation which might be readily identified by classroom teachers? Findings indicate the positive value of students taking part in these short decision-making discussions guided by a structured framework and as part of their normal science classroom activities. Students increase their quality of personal reasoning, and modify their solutions to the issues. The study begins to uncover features about students both as individuals and as members of discussion groups, which can be associated with high quality decision-making about conservation issues, and which teachers might realistically identify. The work calls for the need to cultivate these features and to integrate them appropriately with learning about the scientific concepts that underpin the theory and practice of conservation management. Such integration will facilitate the development of teaching strategies for dealing effectively with the complex topic of biological conservation; not just in terms of science content, but also in terms of how students are expected to engage with the issues. (Contains 3 figures and 3 tables.)