This paper aims to investigate the impact of small-group student-led discussion as a pre-writing task on the writing performance of Iranian intermediate EFL learners. To this end, a quasi-experimental study design was employed in which 80 Iranian intermediate EFL learners were randomly assigned to experimental and control groups, with the former being required to engage in small-group student-led discussions prior to writing paragraphs on a predetermined topic. Their paragraphs were subject to analysis focussed on the components of vocabulary, grammar, content, writing mechanics, and organization. Results indicated that, following the treatment, learners' writing performance improved significantly according to raters' holistic evaluation, as well as specifically in relation to the elements of content and vocabulary. Our study indicates that the socially negotiated nature of learners' interactions can help them engage with and develop a more wide-ranging and in-depth understanding of written content.