This paper focuses upon mathematics teachers' accounts of their professional life in their classrooms. As key social actors in this arena their assumptions about classroom interaction are key structuring devices for the prevailing classroom culture. By examining teachers' accounts of their work in the classroom, using data from two research projects concerned with school mathematics assessment, connections are made between classroom culture and formal assessment procedures. In England, over the last decade since the disruption of the Education Act 1988, there have been debates about teacher professionalism. The institution of a system of national testing and accountability measures has focused attention in these debates on the public dimensions, the outcomes of schooling. In the process, teachers' working relations with students have slipped into the background. In this paper, I turn my attention to these absences by exploring teachers' accounts of their work in assessing their students' mathematical capabilities within the classroom. By highlighting the complex social relations constitutive of classroom culture, I raise questions about the distanced professional position which teachers selectively appropriate in their accounts of students' assessments. I go on to explore the tensions between this position and the teachers' explicit recognition of the more personal interactions which influence both their classroom relations and consequently their judgements of students' achievements.