In this article, we describe a project on reasoning about socio-scientific issues (SSIs), involving French and Australian pre-service science teachers engaged in on-line discussion and development of a wiki. In the research, we developed frameworks for looking at the quality of reasoning about "socially acute" sustainability questions. We found the level of reasoning was enhanced by the cross-cultural exchange, and identified the importance of context in framing reasoning quality. We argue that science teachers could effectively adapt this approach to develop students' scientific literacy and embed the 'science as a human endeavour' strand of the Australian Curriculum in their practice.