Development of linguistic complexity in repeated form-focused classroom tasks: A longitudinal study of Japanese university EFL learners

Abstract

This longitudinal classroom-based study examined how linguistic complexity developed in a Japanese university English as a Foreign Language (EFL) course that integrated task repetition with embedded focus on form. While previous research has emphasised grouplevel trends in complexity development, few studies have explored how learners develop along different trajectories in authentic classroom settings. This study addressed two questions: (1) how does multidimensional linguistic complexity change across repeated form-focused tasks, and (2) what learner profiles emerge from this development? Written texts were collected from 35 beginner-level students (CEFR A1–A2) across eight task cycles over the academic year. Lexical diversity, lexical density, and mean sentence length were analysed, and k-means cluster analysis was used to identify learner profiles. The results showed gradual but non-linear development. Rather than progressing uniformly, learners followed three distinct developmental patterns that reflected different combinations of lexical diversification and syntactic elaboration. These findings suggest that repeated performance tasks with embedded form-focused support create conditions for structural development, while allowing differentiated developmental pathways to emerge. A profile-based perspective may help teachers better understand learner variation and support complexity development in classroom contexts.