Lexical Richness in IB School Students’ L2 Writing

Lexical richness is a dimension of second language (L2) writing, encompassing lexical diversity, density, and sophistication. This quantitative study examines these dimensions in 303 English compositions written by International Baccalaureate students in grades 7–10 at a Chilean school. Corpus-based measures included the type-token ratio, Uber index, and lexical frequency profiling. Results revealed significant grade-level differences in lexical density and diversity, with compositions from grades 9 and 10 generally displaying higher values than those from grades 7 and 8. Lexical sophistication followed a less uniform pattern: productive use of K3 vocabulary was greater in the upper grades, whereas the aggregate sophistication measure did not increase consistently across grades. These findings reveal grade-level variation in lexical performance within a Chilean IB school, where students’ formal exposure to English occurs primarily through school-based instruction. Although these differences cannot be attributed exclusively to the IB curriculum, they are consistent with the contribution of cumulative English instruction across grade levels. The study contributes to research on L2 vocabulary acquisition in bilingual educational contexts and informs pedagogical strategies for enhancing lexical richness in writing. Future research should examine diverse educational settings and the role of explicit vocabulary instruction in lexical development.