Teachers' receptive and productive vocabulary sizes in English-medium instruction

Despite the growing popularity of English-medium instruction (EMI), the conditions for and consequences of teaching and learning academic content through English are poorly understood. The ability of teachers in the EMI environment (i.e. disciplinary or 'content' teachers) to engage students in English is central in this regard since intelligible interaction between the teacher and the students is a precondition for learning when the medium of instruction is English. Across EMI contexts, concerns have been raised about teachers' level of English proficiency (their ability to speak, write, read and listen in English), but research measuring their English proficiency attainments is lacking. This paper focuses on a key dimension of teachers' English proficiency: vocabulary knowledge. Teachers (n = 130) took tests of receptive and productive knowledge of general and academic English vocabulary. The testing revealed significant proficiency variation in the cohorts tested, with some teachers exhibiting very low levels (<3000 words) of receptive and productive vocabulary knowledge. Implications for teaching in EMI are discussed.