The purpose of this paper is to understand how teachers’ identities as assessors in a standards-referenced assessment system may be developed through their participation in online social moderation meetings. In these meetings, teachers negotiate and share their understandings of assessment standards and judgement decisions. In particular, the paper focuses on the relationship between the technology, the moderation processes and teachers’ development in this assessment system. This paper draws on sociocultural theories of learning to analyse the qualitative data collected through observations of 11 online moderation meetings and interviews with the teachers involved in these meetings. The results provide insights into the mediating role of the technology with regard to teachers’ development of shared meanings and common practices within a standards referenced assessment system.