This study examines the impacts of dyadic collaborative writing on the academic writing performance and writing confidence of upper primary ESL students in Malaysian vernacular schools, based on Krashen’s Affective Filter Hypothesis and Vygotsky’s Sociocultural Theory. Writing remains one of the most difficult linguistic abilities, especially when the predomination of conventional teacher-centred methods in many Malaysian vernacular classroom settings restricts the exposure to process-oriented writing, exchange of ideas, and peer engagement. 28 students of Year 4 to 6 were split into control and experimental groups as part of a mixed-method quasi-experimental design. Throughout the four-week intervention, the experimental group experienced dyadic collaboration during narrative writing assignments, whereas the control group worked individually. Data from writing confidence surveys, pre-test and post-test on narrative writing, weekly teacher observations, and focused-interviews were gathered. Quantitative results showed that students in the experimental group surpassed the control group in terms of idea development, terminology diversity, and rational flow, alongside a significant rise in writing confidence. Qualitative data acquired via the teacher observations and focused interviews revealed that students in the experimental groups reported feeling more engaged, confident, and more driven when writing assignments due to peer support and joint responsibility. The study underscored the emphasis on student- centred, process- oriented writing instruction and recommends further research across distinctive age groups, genres, and digital platforms.