In contexts of both English as a second language (ESL) and English as a foreign language (EFL), there is an ongoing effort to incorporate online graded reading materials into extensive reading programs designed for second language (L2) learners. However, it remains largely unknown to what extent these texts are suitable for L2 learners in terms of lexical demand. Based on a large corpus comprising nine levels of online graded reading materials, the present study examined the lexical profile of these texts at both corpus and grade levels. Results of our study showed that to achieve minimal and optimal comprehension of these materials at the corpus level, learners are expected to know 3,000 word families and 6,000 word families respectively plus proper nouns, marginal words, transparent compounds, and acronyms. As for the lexical demand across different grade levels, it was found that the lexical demand increases slightly and steadily as grade level increases. Overall, these results indicate the potential value of online graded reading texts as extensive reading materials for lower-level and mid-level L2 learners. Implications for L2 teaching and learning are also provided.
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