Studies in science education have explored contextual features that facilitate students' active participation in discussion in argumentation activities. Based on this literature, we aimed to explore students' practices as they shifted their epistemic practices from unproductive to collaborative meaning-making discussion in an argumentation activity in a science classroom. We examined the discursive interactions of a small group with students who attempted to engage in interaction with one another, facilitating the negotiation of group members' positional framings as collaborative contributors during an argumentation activity. Although the students suggested ideas and engaged in interactions, the students' interactions were first dependent on a student holding higher epistemic authority (a polarized collective zone of interaction). The students' shift to collaborative contributors was shown in separate zones of interaction from a student with higher epistemic authority, led by a student who repeatedly attempted to elicit other students' reasoning. Then, at the end of the activity, this zone of collaborative contributors expanded to all of the group members, and the students jointly developed the reasoning (a collective zone of interaction). This finding indicates the importance of facilitating students in recognizing not only themselves but also one another as also potential contributors. With such acknowledgment, the students can elicit one another's ideas, facilitating them in positioning themselves as collaborative contributors in argumentation activities. We discuss the meaning of being collaborative contributors and the significance of students' role in shifting their positional framing.