Environmental and sustainability issues prevail in modern society. Southern Africa, where this study is based, is one of the regions most at risk from intersecting issues of climate health risk, and poverty-related ills. Education has the potential to facilitate catalytic transformation of society through development of understandings of these intersecting environment and sustainability concerns, and to support engagements in more sustainable social practices oriented towards the common good. This requires a rethinking of education within a wider common good frame. It also has implications for how quality education is considered. However, little is said of how this could be done, especially in teacher education. The paper shares two cases of teacher educators' change project experiences, as they emerged via professional development support and the mediatory processes applied in courses conducted by the Southern African Development Community Regional Environmental Education Programme (SADC REEP) aimed at enhancing professional capacity of teacher educators and other environmental educators for mainstreaming environment and sustainability education (ESE) 1 . These courses are framed using a change project approach, and involve teacher educators as main participants. In-depth data were generated from interviews with two teacher educators, their assignment write-ups, and observations of their teacher education practice. Realist social theory, particularly the principle of emergence, was used to trace the emergence of change in teacher education practice. Sociocultural learning theory was used to explain mediation of learning-oriented changes in teacher education practice. We illustrate how the change project model and approach contributed to mediating change in practice, showing emergent attributes of capacity for mainstreaming ESE and elements of a concept of quality education among course participants oriented towards the common good. In conclusion, we argue that ESE seems to be a sensitising construct for initiating and sustaining change for ESE in teacher education. In addition, the change project has proved to be a potential vehicle for mainstreaming the notion and practice of ESE into social systems and teacher education 1 In this paper we use the term, environment and sustainability education (ESE), to indicate that it includes an emphasis on environmental education(EE), and education for sustainable development (ESD). ESE, as used in this paper, includes a strong focus on the interrelated nature of environmental, societal, political, and economic concerns, and the way in which this term is used is oriented towards the wider common good. practices. We argue that reflexive ESE praxis provides a sensitising focus, initiating quality education with humanising properties necessary for the common good.