Pre-service teachers' conceptions of assessment have received relatively little attention in research concerned with professional development in initial teacher education. These conceptions, alongside others regarding teaching and learning, however, have a great impact on future teachers' instructional practices. In this study, the authors examine conceptions of assessment indirectly, by analysing 79 Finnish pre-service subject teachers' narratives of students' failure. Their findings reveal four major conceptions: (a) assessment is about feedback and reflection; (b) assessment needs to be personalised and demonstrate students' learning; (c) assessment should take into account students' invested effort; and (d) assessment fails to measure students' success or failure. These findings provide a qualitative insight into and extend both research on teachers' conceptions of assessment as a vital aspect of assessment literacy and research on pre-service teachers' conceptions in particular. The relevance of these findings for future teachers' professional development is discussed.