School is assumed to equip students with subject knowledge and contribute to their development as human beings and democratic citizens as well. In this article, the democratic dimension of the teaching assignment is brought to the fore, and an analysis tool for investigating students' conversations on socioscientific issues that emphasises democratic aspects is presented. The DEQUAL-tool, where the acronyms stand for DEliberative QUALities, comprises both the content-related and formal aspects of the conversations, with a specific emphasis on the collective expressions of democratic qualities like questioning, consideration for others and conveying different dimensions and arguments. DEQUAL is based on an intersubjective and communicative understanding of democracy and meaning-making, and is theoretically inspired by John Dewey's and Jurgen Habermas' views on these matters. The development and function of DEQUAL is clarified using excerpts from upper secondary school students talking about how living in a certain place influences the greenhouse effect. By pointing out characteristics, strengths and weaknesses of students' group-conversations, this methodological proposal can provide further guidance for an integrative understanding of the teacher's assignment in science education. (Contains 3 tables and 8 notes.)