Enhancing EFL students' argumentative writing with collaborative argument mapping in the GenAI era

English as a foreign language (EFL) teachers now face a growing conundrum. Although generative artificial intelligence (GenAI) can assist learners in producing fluent text, overreliance on GenAI may risk undermining students’ independent writing development. The present study investigated the effect of collaborative argument mapping (CAM), a non-GenAI pedagogical scaffold, on EFL learners’ argumentative writing. Adopting a mixed-methods research design, we integrated Kialo Edu, an online CAM platform, into the argumentative writing instruction for 50 Chinese postgraduate EFL students. Repeated measures analysis of variance showed no significant improvement in students’ writing scores; however, a significant improvement in global cohesion was revealed. Further, students reported: (a) strengthened critical thinking and argument structuring; (b) generally positive platform experiences that clarified relations among claims, reasons, and evidence; and (c) more deliberate writing processes. Nevertheless, they also noted some challenges (e.g., information load, uneven attention to language forms). The findings suggest that Kialo-mediated CAM can support EFL learners’ discourse organization and foster perceived gains in critical thinking and argument structuring. Practical recommendations for optimizing the CAM-based writing pedagogy are also proposed.