The Teachers Conceptions of Assessment Inventory was used to investigate New Zealand teachers' beliefs about assessment. The participating sample comprised teachers who work almost exclusively at the senior level of high school and are responsible for school-based assessment programmes that contribute at least 50% of students' final grades towards qualifications. Factor analyses showed that these teachers had conceptions of assessment that were more similar to those of teachers in countries with qualifications systems based on high-stakes examinations than to a more general sample of participants in previous New Zealand research. In particular, there was a strong positive correlation between the formative views of assessment and the view that assessment promotes student accountability. The study revealed ecological influences on teachers' conceptions of assessment, as well as tensions that arise between formative and summative views of assessment, when teachers are responsible for assessment contributing to national qualifications.