The recurrent reminders that climate changes are man-made and demand action, calls for the development of novel teaching approaches which besides transferring information, solutions, and values, also allow students to engage in critical reflections and through common inquiries strengthen their decision-making abilities and sustainable commitment. Answering the question: What characterizes Danish Mercantile upper secondary school students' conversations about sustainability issues? this article analyses students' (n = 128) ability to engage in dialogic sustainability inquiries supported by an interview guide in a Video Club setting as part of the school context, but without a teacher present during the recording. 32 Video Club conversations were coded with an operationalization of Neil Mercer's and Robin Alexander's conception of 'dialogue'. The students view sustainability as related primarily to environment and climate, they share relevant ideas but lack abilities to establish common understandings of central concepts. Video Clubs can support students' practice of dialogic skills and sustainable commitment in a setting free from teacher control and moralization.