Over the past decades, the use of strategies by language learners has been the subject of considerable research. Yet comparatively few studies have examined the direct effects of strategy instruction on the actual writing strategy use of learners, with specific comparisons involving students at different levels of proficiency. This study examined if focused writing strategy instruction can increase the use of writing strategies by EFL learners. Using a mixed-methods design, 64 undergraduate learners in Iran were divided into experimental and control groups. The experimental group received strategy-based instruction grounded in Oxford’s (1990) framework, while the control group received conventional writing instruction. Data were collected through pre- and post-tests, stimulated recall protocols, and a validated strategy-use questionnaire. Findings from a mixed between-within ANOVA revealed significant time-group- proficiency interactions, indicating that strategy instruction benefited learners differently across proficiency levels. Qualitative analysis further highlighted how learners integrated strategies into their writing practices. The results have implications for tailoring writing instruction to proficiency-specific needs.
