There is growing concern about whether mandated instructional materials are accessible to learners at the level intended by the curriculum, particularly in secondary education where textbooks play a central mediating role. Building on this concern, the present study examines curriculum accessibility by focusing on the alignment between learners’ vocabulary readiness and the lexical demands of nationally prescribed English textbooks. Drawing on an assessment-informed approach, the study integrates learners’ vocabulary test results with a corpus-based analysis of a widely used textbook series in China. The findings reveal a systematic misalignment between learners’ vocabulary development and textbook lexical demands. While mastery of the most frequent vocabulary is largely secured, readiness beyond this level varies substantially by grade and constrains access to textbook-mediated instruction, particularly for students in Grade 10. To address this gap, the study identifies a curriculum-supporting vocabulary set that substantially improves lexical accessibility across textbooks. The findings highlight the value of using vocabulary assessment as diagnostic evidence for evaluating curriculum accessibility and informing textbook design, instructional support, and curriculum planning in secondary English as a foreign language (EFL) contexts.
Li et al. (2026) studied this question.