Young people's conversations about environmental and sustainability issues in social media and their educational implications are under-researched. Understanding young people's meaning-making in social media and the experiences they acquire could help teachers to stage pluralistic and participatory approaches to classroom discussions about the environment and sustainability. "The aim" of the article is to explore the characteristics of meaning-making in young people's conversations about environmental and sustainability issue in social media, more precisely in an online community. The study takes a public pedagogy and citizenship-as-practice approach and uses Epistemological Move Analysis. The conversation are shown to be argumentative, sophisticated, elaborative and competitive and create an educational situation in which facts about the world and moral and political values and interests are confronted and argued. The findings raise questions about pluralistic and participatory approaches and the staging of classroom conversations in environmental and sustainability education.