A particular framework of teachers' conceptions about assessment in school is presented. Fifty teachers of primary and secondary school were interviewed. Results of a qualitative analysis allowed building a model of conceptions of assessment. This model comprises four dimensions about the effects of assessment on: teaching, learning, accountability of teachers and schools to different audiences and stakeholders, and the certification of achievement. These conceptions, unequally distributed, show some tendencies that might be linked to the intrinsic tension between the by-default co-occurrence of both pedagogic and societal functions of assessment in school, and to difficulties of implementing assessment for learning practices. (Contains 2 figures and 1 table.)