Eastern Heights Primary School's involvement with research on assessment for learning began in 1998 with a focus on technology education as a new learning area. The initial research outcomes highlighted the impact that teachers' pedagogical content knowledge has on classroom and school practices in assessment for learning. In the subsequent years, enhancing teachers' planning, teaching and assessment knowledge and practices were key foci, as were developing teachers' understandings of subject ideas and how these might be translated to best fit their students. Teachers' formative interactions and summative assessment practices became focused on encouraging and supporting student engagement with key subject ideas in order to move student learning forward. For effective learning to occur, it was crucial for teachers to have conversations with students around these ideas. The impact of the intervention programme on teachers' assessment for learning practices and student learning was so significant that changes were made to classroom practices at the wider school level in technology, and were also incorporated effectively into science programmes and other curriculum areas. This article describes why the research and intervention programmes undertaken with a few teachers impacted positively on a school-wide basis. The school culture, the positive research outcomes and the nature of the research process contributed to school-wide changes in assessment for learning practices. This long-term research programme provides insights into how enhanced assessment for learning practices at the individual teacher level might expand to a school-wide level.