A large-scale longitudinal study of syntactic complexity development in EFL writing: A mixed-effects model approach

This study examined the longitudinal development of syntactic complexity with a large-scale corpus of EFL (English as a foreign language) compositions written by the same group of 1081 intermediate Chinese university students over a time span of four consecutive semesters in two academic years. The compositions were analysed for the longitudinal trajectories of syntactic complexification over time and for proficiency level differences, and genre differences. It was found that length-based measures, measures of coordination, and those of phrasal sophistication significantly increased while measures of clausal subordination significantly decreased from the first to the fourth semesters. Interestingly, students' writing style was found to become more formal and exhibited more prominent features of academic prose over time. Furthermore, students' proficiency level and genre showed significant main effects on most of the syntactic complexity measures. Our findings complemented existing research on writing development patterns with large-scale and longitudinal evidence. Some possible explanations in relation to these findings were discussed. In addition, implications for teachers and researchers of EFL writing were offered.