Incidental and planned focus on form in EMI science classes: possible role of teachers’ past ESL/EFL teaching experience

English medium instruction often bears the promise of providing a meaning-focused approach to L2 learning alongside content learning. However, EMI teachers are found to resist their role as language teachers. A common reason is they are typically content specialists with no language training or teaching experience. This study investigates when EMI teachers do possess ESL/EFL teaching experience whether there is a difference in their integration of language during teacher-whole class interaction. The SLA concept, focus on form, is adopted to analyze the incidental and planned focus on form in 30 video recorded EMI science classes taught by 15 native speakers of English teachers (NSTs), where five of them possess past ESL/EFL teaching experience. Findings show teachers with such experience used more focus on form, and two teachers with extensive past ESL/EFL teaching experience had lengthy planned focus on form. Suggestions are made in optimizing focus on form in EMI classes.