The present study analyses the impact of negotiation processes on activating argumentative resources for decision-making in a socioscientific issue (SSI) in biology classes. The research focuses on the potential of group-based negotiation processes to activate the use of relevant argumentative resources without any prescribed or explicit instructions on these resources and arguments. In the corresponding intervention with a pre-post-design, students are encouraged to reason and weight their own arguments, which are based on protecting local biodiversity. The students have to reason and weight individually (pre-phase) immediately before they discuss their own reasoning and weighting with others in groups (treatment). The students have to then, once again, reason and weight their arguments individually (post-phase). The students are instructed, during these three steps (pre-phase, treatment, post-phase), using an educational tool, target-mat, which structures the reasoning and weighting visually, but does not prescribe the way of argumentation. By analysing the students' argumentative resources, normative and fact-based elements can be measured immediately before and after the negotiation process. In terms of the pre-phase, the use of differing and appropriate argumentative resources can be analysed in relation to different arguments. The pre- and post-comparison reveals relevant changes leading to a substantial increase of the quality of reasoning. Therefore, in a student-centred decision-making process with minimal guidance, students are encouraged to become aware of the appropriateness of different argumentative resources.