Alireza Sohrabi Ashour - Department of English Language and Literature, Science and Research branch, Islamic Azad University, Tehran, Iran.
Masoomeh Estaji - Department of English Language and Literature, Science and Research branch, Islamic Azad University, Tehran, Iran.

Individual differences in writing quality may be accounted for by a number of factors among which one can refer to linguistic factors in general and syntactic complexity in particular. However, only a limited number of research studies have been undertaken to examine the degree of contribution of this linguistic feature to the writing quality of Iranian advanced EFL learners. Therefore, the present study is intended to explore the impact of heightening syntactic maturity via manipulating subordinating conjunctions upon academic writing quality. To this end, a total number of 30 participants- were selected (both male and female, mostly aged 18-24, Iranians and L1 speakers of Persian) from among 72 advanced EFL learners after administrating a Michigan Test of English Language Proficiency. These participants were taught how to manipulate complex syntactic structures in their essays. This study adopted a quasi-experimental design and collected data through the administration of IELTS academic writing tests. A paired samples t-test analysis was run to determine the degree of improvement in this specific linguistic feature, i.e., the syntactic complexity on the academic writing quality by measuring the Mean Length of T-unit (MLTU) value of the participants’ essay. The results of the study uncovered that teaching how to manipulate and use subordinating conjunctions led to the enhancement of the syntactic complexity of the participants’ essays. Likewise, teaching how to manipulate subordinating conjunctions contributed to the improvement in the writing quality of the participants’ essays and thereby their overall writing quality. These finding question what Kuiken, Vedder, and Gilabert [1] have indicated in a correlational study that examined the decisions made by the raters to grade the students’ essays and concluded that they may have been influenced more by the range of vocabulary used by the participants and the accuracy of production than by the linguistic complexity of the text. Moreover, the results of the study verified and supported Hillocks’ (1986, as cited in Beers & Nagy [2]) contention that the knowledge of complex syntactic structures is particularly effective in improving the learners’ L1 writing quality. Finally, the findings were discussed from the perspective of pedagogical implications, syllabus design, and language testing

writing quality, syntactic complexity, Iranian advanced EFL learners, Mean Length of T-unit