There exists a gap between what second language acquisition research has to say and what teachers do in the classroom. As part of an attempt to bridge this gap, this study is driven by the motive to understand how pedagogical innovations such as task-based language instruction can be influenced by teacher beliefs. Drawing on the perspective of research on teachers’ thinking which aims to inform language teaching pedagogy and teacher education, the study employed multiple data sources (focus group, lesson plan, and stimulated recall interview) to tap into the conception of six Vietnamese EFL instructors regarding language output and interaction. Cross-case analysis showed that most of the teachers geared language output and interaction activities towards achieving a targeted linguistic aim. Further analysis revealed that this view reflects a synthetic, product-oriented conception of teaching and learning by skill-building, and is in line with traditional approaches which emphasise transmission style and form instruction.This fnding implies that constructivist perspectives on teaching such as task-based language instruction may run counter to teachers’ existing conception of teaching. The implementation of task-based instruction thus needs to consider negotiating between supporting teachers to focus on meaning and the need for form-focused instruction.