The current study sought to explore the impact of SFL-oriented register instruction on Iranian EFL learner’ writing performance with a central focus on their English proficiency level. As its secondary aim, the study delved deeply into the learners’ perception of the register-based instruction. To these ends, 50 intermediate and 50 advanced Iranian EFL learners were selected randomly and assigned to four groups: two experimental and two control groups. Employing an experimental pretest/posttest design, the learners of the two experimental groups received instruction on the three components of register; that is, field, tenor, and mode along with the implementation of a three-phase teaching/learning cycle, whereas the learners in the control groups were exposed to a conventional writing instruction. Quantitative analysis of the learners’ writing performance on the pre- and posttest measures revealed the contributory role of register instruction in improving Iranian EFL learners’ writing performance, regardless of their English proficiency level. Furthermore, having been surveyed through a researcher-made questionnaire, the advanced and intermediate learners expressed their positive attitude towards the instruction. The findings highlighted the necessity of superseding the traditional linguistic-based writing instruction by a contextual and situational teaching methodology similar to what has been implemented in the current study.
