<![CDATA[Creative writing is a fundamental component of language education because it develops creativity, communication skills, critical thinking, and expressive competence. However, Indonesian language classrooms still face challenges in fostering creative writing due to teacher-centered instruction, limited collaboration, and insufficient opportunities for students to generate, refine, and communicate original ideas. This study examined the effectiveness of collaborative writing in improving students’ creative writing skills and explored the mechanisms through which collaborative learning enhances writing performance. A sequential explanatory mixed-methods design involved 320 secondary school students in a quasi-experimental pretest–posttest control group study. Quantitative data were analyzed using descriptive statistics, independent-samples t-tests, repeated-measures analysis of variance, structural equation modeling, mediation, and moderation analyses. Qualitative data were obtained through classroom observations, semi-structured interviews, reflective journals, and document analysis. The findings showed that collaborative writing significantly improved idea originality, narrative organization, vocabulary richness, grammatical accuracy, writing motivation, classroom engagement, and overall creative writing achievement compared with conventional instruction. Peer-feedback quality and metacognitive regulation partially mediated the relationship between collaborative writing participation and writing performance, while classroom engagement strengthened these effects. Collaborative writing therefore offers an effective pedagogical framework for enhancing creative expression, language proficiency, reflective learning, and sustainable literacy development in Indonesian language classrooms.]]>
