The International Baccalaureate’s expansion of subject learning in English: An analysis of the diploma programme in Japan

Abstract

The implementation of the International Baccalaureate (IB) is expanding globally. In Japan, the number of schools offering the IB has increased from 27 in 2014 to 122 in 2025, including both public and private schools. The Dual Language Diploma Programme (DLDP) of the International Baccalaureate Organization, promoted by the Ministry of Education, Culture, Sports, Science and Technology in Japan, provides at least two of the six courses in English and the rest in Japanese. This study explores the English-medium instruction (EMI) in DLDP high schools in Japan. Seventeen teachers from three public schools offering the programme within the Japanese educational framework were interviewed to qualitatively document and examine the state of English instruction in Japan. Teachers reported using English and Japanese flexibly according to their students’ needs and adjusted instructional emphasis based on subject-specific characteristics. Notably, mathematics and science instruction prioritised computational processes, which consequently expedited calculations when conducted in Japanese. A gradual transition from Japanese to English, beginning with basic content in Japanese, was shown to be effective for student learning. Teachers’ narratives revealed that subject learning in English is influenced by both assessment demands and the socio-cultural relevance of each subject. This study contributes novel insights, as it is among the first to explore long-term EMI practice through subject-specific teacher perspectives in Japan. The findings provide valuable information for IB schools implementing second-language instruction worldwide.