Does instructional language matter in CLIL? A study of learner proficiency and affective factors

This study examines the English language proficiency and affective factors of Japanese university students enrolled in medical programs taught in English (CLIL) (n = 44) and those taught in Japanese (L1-supported CLIL, n = 61). Pre- and post-study questionnaires, administered over a 14-week semester, measured speaking and writing proficiency, L2 speaking and writing anxiety, language learning enjoyment, international posture and willingness to communicate. The results show that both CLIL and L1-supported CLIL students experienced gains in speaking proficiency and a reduction in L2 speaking anxiety. The CLIL group demonstrated a decrease in L2 writing anxiety and an increase in willingness to communicate, while the L1-supported CLIL group showed an increase in international posture. This study reveals that L1 instruction in certain aspects of the first year of the CLIL curriculum appears to provide a supportive environment for lower-proficiency students to develop L2 proficiency and an international posture. Pedagogical implications are discussed in relation to the importance of selecting instructional language according to students’ L2 proficiency levels when designing CLIL programmes.