ABSTRACT Systems thinking is essential for understanding wicked real-world problems and suggesting solutions. This is the case for addressing socioscientific issues (SSI) that involve inter-related personal, socio-political, cultural, scientific, economic and moral dimensions. It is challenging for teachers to support students in adopting and practising systems thinking when they explore SSI. In this study, we tested the extent to which causal loop diagramming (CLD) developed students’ systems thinking. We examined a 2-week teaching unit that used a computer-based CLD tool to foster students’ systems thinking about obesity in a first-year university general education course. Ninety-six students from a variety of majors/disciplines participated in this study. They worked in groups and engaged in reading news, proposing actions while creating causal loop diagrams about factors that contributed to obesity and approaches to tackle the issue. We analysed their pre-, mid-, and post-unit causal loop diagrams (3 × 26 groups) and weekly reflective memos. The data revealed their significant shift towards a systems approach of thinking. The reflective memos showed that the shift was afforded by cycles of construct–revise–use as they created the diagrams. The findings suggest the potential of causal loop diagramming to foster systems thinking in the sense-making and decision-making of SSI.