Corpus-informed evaluation of efl textbook–examination alignment in Vietnamese upper-secondary reading: evidence from text complexity indices

Vietnamese upper-secondary students use the Global Success English textbook sequence, while their end-of-school reading performance is assessed through the National High School Graduation Examination. This study examined the alignment between 72 textbook passages from Grades 10–12 and 14 examination passages from 2020–2026. A quantitative corpus-based descriptive-comparative design compared lexical diversity, lexical sophistication, syntactic complexity, cohesion, and readability. At the overall corpus level, lexical and readability measures showed no differences after Holm adjustment, although examination passages varied across periods. More consistent differences concerned cohesion and clause organization: examination passages contained fewer connectives and a higher density of dependent clauses. The findings indicate selective rather than uniform alignment and show how multidimensional corpus evidence can support materials evaluation, language assessment literacy, and EFL reading instruction in a high-stakes context.