This study adopted a dynamic approach to examine the development of lexical and syntactic complexity in the second language (L2) writing of a cohort of advanced-level students at a Chinese university over a four-month semester. Using six progress-sensitive complexity measures, the research analyzed both group and individual data to identify patterns of change and explore phase transitions in learners’ developmental trajectories. The findings reveal dynamic, non-linear trajectories characterized by marked inter-learner variation and temporal asynchrony across domains of complexity, collectively indicating a shift toward more concise, academic prose. Longitudinal evidence and mixed-effects models showed that while feedback demonstrated minimal effects on short-term complexity gains, it served as a trigger for long-term complexity development. Qualitative data revealed that the effectiveness of feedback depended on the nature of feedback (i.e., type and cognitive demand) and learners’ engagement. These findings offer valuable theoretical insights into the L2 complexity development mechanism and underscore the need for pedagogy that teaches advanced stylistic conventions while cultivating the engagement and feedback literacy necessary for learners to effectively incorporate instructor and peer input.
Wang et al. (2026) studied this question.