It is well-documented that metacognitive instruction is significant in helping L2 learners generate written texts (Wenden, 1998; Xu, 2023). However, little is known about how metacognitive instruction in conjunction with collaborative writing interventions would contribute to learners' individual writing development. To fill the research gap, we recruited 62 Chinese EFL learners from two classes, who were randomly allocated to either an experimental group or a control group. The experimental group received metacognitive instruction for collaborative writing before engaging in collaborative writing interventions, while the control group received normal instructions. Improvement in writing performance was gauged through three essay writing tasks sourced from the IELTS writing test bank, measuring performance across dimensions including content, organisation, vocabulary, language use, mechanics, and overall scores. Results indicated that the combination of metacognitive instruction and collaborative writing significantly enhanced participants' individual writing scores. This study provides empirical support for the effectiveness of incorporating metacognitive instruction with collaborative writing, emphasising its positive impact on writing development and the promotion of learner self-regulation.