This article outlines a critical position in relation to education for sustainable development referring to a socio-ecological approach to environmental education. This approach was developed in a cooperative research process with pre-academic secondary schools over several years in Switzerland. For 13 years our research group has been the one in Switzerland to systematically research curriculum and professional development in environmental education in secondary schools. The group was established at the Swiss Federal Institute of Technology in Zurich (ETHZ) supported by funding from the Swiss National Foundation for Scientific Research, and from 1998 proceeded with research projects at the Institute for Teacher Education (upper secondary level) at the University of Zurich. Case studies were carried out to explore the potentials and constraints which teachers and students meet when working with environmental issues. Two case studies from different research phases are shown which illustrate how both teachers and learners are challenged to cope with increasingly unstructured and unknown situations, pluralistic and controversial perspectives, and with the critical role of science in society. Outcomes are discussed in the light of the social process of sustainable development.