Evaluating Academic Reading Input in Vietnamese EFL Textbooks: Lexical, Syntactic, and Cohesive Evidence for Materials Design and Classroom Pedagogy

Abstract

The acquisition of academic vocabulary and complex linguistic structures is essential as learners move from general English proficiency toward academic literacy. In many Asian EFL contexts, textbooks remain a major source of lexical and structural input. This study presents a multi-dimensional corpus-based evaluation of 72 reading passages in the Global Success textbook series for Vietnamese upper-secondary students. Using TAALED, TAALES, TAASSC, and TAACO, the passages were analyzed as separate text-level units to examine lexical diversity, lexical sophistication, syntactic complexity, and cohesion across grades. Mean Academic Word List (AWL) coverage showed a non-linear descriptive pattern, declining from 5.90% (SD = 2.98) in Grade 10 to 5.41% (SD = 2.94) in Grade 11 before rising to 6.95% (SD = 3.52) in Grade 12. Mean Measure of Textual Lexical Diversity (MTLD) scores increased descriptively from 70.64 (SD = 14.55) to 74.04 (SD = 17.50) and 79.24 (SD = 21.15), respectively. However, Kruskal–Wallis tests found no statistically significant between-grade differences in AWL coverage or MTLD. Syntactic and cohesion measures also showed substantial passage-level variation, with only small descriptive differences in grade-level means. Overall, the findings do not support a uniform progression across Grades 10–12 and are better characterized by considerable heterogeneity among individual passages. The study demonstrates how text-level corpus analysis can identify areas that may warrant consideration for additional vocabulary and structural support in Vietnamese upper-secondary reading instruction.