This study seeks to investigate how lexical, phraseological, and syntactic complexity features influence the argumentative writing scores of English as a foreign language (EFL) beginning-level learners over two semesters. The participants included 42 EFL students at the university level in a Japanese university. They generated six timed second language (L2) argumentative essays, which underwent subsequent analysis for lexical, phraseological, and syntactic complexity features. The findings suggest that linguistic complexity features significantly predicted L2 writing scores over time. Specifically, beginning-level learners attained higher scores in their L2 argumentative essays when incorporating more sophisticated content words, as demonstrated by elevated age-of-acquisition scores, increased phraseological sophistication utilizing frequently employed bigrams from an academic reference corpus, and enhanced global syntactic complexity through the use of longer T-units. In summary, this study emphasizes longitudinal connections between L2 writing scores and linguistic complexity.
II. Literature Review