In this paper, we utilize a discursive psychological approach to further explore agency and structure in science education research. The aim of our research is to understand how we can provide opportunities for marginalized students in preservice elementary teacher education in an Australian university to become agentic concerning environmental sustainability. Preservice teacher agency in this study is understood as the positioning of preservice teachers as responsible for their action. Responsibility can be indexed using grammatical devices including pronouns. Structure and agency are analyzed as constantly remade through socially meaningful action and the smallest course of our analysis is the social act. In this way, we have treated agency and structure as a dialectic but avoided their central conflation. Our findings emerged from the analysis of open ended reflective journals written by the preservice teachers related to taking action in their daily lives to reduce their ecological footprint during a semester-long science course. We select an instrumental case, Ecocarmie, to illustrate our findings and the potential of our discursive psychological approach for further research in this area. In our analysis, we show how Ecocarmie self-positions in the public domain of Tumblr as pro-environmentally engaged, drawing upon social and material resources and discuss the implications of our study for preservice teacher education in EfS.