Collaborative discussion-supported writing (CDSW) provides opportunities for students to develop arguments and counterarguments through peer communications with a goal to promote a high-quality argumentative essay. Cognitive scaffoldings can be used to facilitate students' collaborative discussions. However, there is a lack of investigation on the utilisation of cognitive scaffoldings to facilitate CDSW, which limits valuable insights for the instructional design of cognitive scaffolding. This research designed collaborative discussions to support argumentative essay writing at a Chinese senior high school, with three cognitive scaffoldings (i.e. minimal, idea-centred and idea-centred, argumentation-oriented scaffoldings). Results revealed the best effect of the idea-centred, argumentation-oriented scaffolding on collaborative learning processes and performances, compared to the minimal and idea-centred scaffoldings. Based on the results, this research proposes that knowledge construction elements, engagement levels and additional supports should be considered in instructional design of cognitive scaffoldings to improve collaborative learning.