From Words to Writing: Vocabulary Growth and Its Impact on L2 Composition Over Time

A body of research has examined the relationship between vocabulary knowledge (VK) and English as a Foreign Language (EFL) writing proficiency. However, it is still unclear how the vocabulary-writing relationship develops over time. This longitudinal study followed 154 Chinese university learners over an 8-month period using the same battery of vocabulary and writing tests. Pearson correlations on bootstrapping and Linear Mixed-effects Models (LMM) were used for data analyses. The results showed that learners made substantial gains in receptive size, while productive size remained at the 2,000 to 3,000 word level, despite a moderate increase. Productive derivative knowledge also showed moderate improvement. Further analyses revealed a developmental shift: receptive size was more strongly related to writing performance at the earlier stage, whereas productive size and derivative knowledge became stronger predictors later. In contrast, vocabulary depth (collocations and synonyms) showed little improvement and did not predict writing performance. These findings enhance our understanding of the dynamic relationship between vocabulary and writing and highlight the importance of fostering productive vocabulary and depth of knowledge through both formal instruction and informal exposure.