Tracing Lexical and Discourse Development in a Chinese EFL Learner: A Longitudinal Case Study

In this longitudinal single-case study, the English writing development of one Chinese senior high school learner was examined through three picture-based narratives. The analysis focused on how growth unfolded in two areas: vocabulary use (“word” system) and the development of propositional content (“mind” system). Lexical change was tracked using the type–token ratio, and discourse expansion was examined by identifying idea units. Over the six-month period, TTR rose slightly (0.52 ? 0.54), while idea units showed a more noticeable increase (14 ? 24 ? 30). Follow-up interviews indicated a shift in the learner’s orientation—from mainly completing tasks out of obligation to taking a more self-directed interest in English, partly influenced by exposure to English-language media. These developmental patterns were interpreted within a dynamic systems perspective, which helps explain the uneven and sometimes nonlinear nature of change across linguistic and affective dimensions. The study also reflects on methodological choices and offers implications for EFL instruction and for future longitudinal work on individual learner development.