Language proficiency, vocabulary knowledge, and individual factors in predicting academic achievement: insights from the Vietnamese EFL context

Abstract This study contributes to research on predictive validity by examining both linguistic factors (language proficiency and vocabulary knowledge) and individual factors (autonomous learning activities, language learning attitudes, and course perceptions) in predicting academic achievement in English-medium instruction (EMI) programmes in Vietnam, where standardised proficiency tests show limited predictive power. Data were collected from 105 undergraduate students at a teacher-training institution in southern Vietnam, who completed the Pearson Test of English Academic and a Vocabulary Size Test. Hierarchical linear regression showed that combined language proficiency and vocabulary measures predicted academic achievement moderately well, outperforming either measure alone. Partial least squares structural equation modelling further indicated that the three individual factors influenced academic achievement indirectly through their effects on language proficiency and vocabulary knowledge. These findings highlight the value of using multiple measures–including language proficiency tests, vocabulary assessments, and individual factors–for admission and screening in EMI programmes.