Syntactic complexity in adapted extracurricular reading materials

Extracurricular reading is important for language learning since it is not just beneficial for vocabulary and grammar acquisition, but also useful for other aspects such as reading comprehension. Previous research has focused on the role of linguistic features such as syntactic complexity in adapted textbooks, while little attention has been paid to that in other reading materials such as extracurricular ones. This study examined the syntactic complexity in adapted extracurricular reading texts at five difficulty levels based on five machine learning algorithms. The results showed that the adapted texts differed significantly across the five levels in terms of syntactic complexity, with large effect sizes. In addition, three indices of syntactic complexity, i.e., DC/T, MLS, and CN/C, were found to well distinguish texts at different levels. The findings of the present study have significant implications for the adaptation of language learning materials such as extracurricular reading texts and test materials.