The integration of socioscientific issues (SSI) in science education calls for emphasizing dialogic classroom practices that include students' views together with multiple sources of knowledge and diverse perspectives on the issues. Such classroom practices aim to empower students to participate in decision-making on SSI. This can be accomplished by enhancing their independence as learners and positioning them as legitimate participants in societal discussions. However, this is a complex task for science teachers. In this study, we introduce positioning theory as a lens to analyse classroom discourse on SSI in order to enhance our knowledge of the manners by which teachers' interactions with students make available or promote different positions for the students, that is, different parts for the students to play as participants, when dealing with SSI in the classroom. Transcripts of interactions between one teacher and six student groups, recorded during two lessons, were analysed with respect to the positioning of the students as participants in the classroom, and in relation to the SSI under consideration. The results show that the teacher-student interactions made available contrasting student positions. The students were positioned by the teacher or positioned themselves as independent learners or as dependent on the teacher. Furthermore, the students were positioned as affected by the issue but as spectators to public negotiations of the issue. Knowledge about the manner in which teacher-student interactions can function to position students seems important for dialogic classroom practices and the promotion of student positions that sustain the pursuit of intended educational outcomes.