For over two decades, New Zealand primary schools teachers have been confused and stressed about assessment. Research carried out between 1998 and 2000 showed that teachers were not assessment literate. They didn’t have a good understanding of assessment theory. The political and educational purposes of assessment were in conflict with each other. Teachers were getting mixed messages about what they should be doing. The research found that teachers prioritised summative assessment and assessment for accountability although most teachers could see the considerable educational benefits of adopting formative assessment practices. They appeared to lack an understanding of how to translate such approaches successfully into classroom practice. Since then most teachers have had opportunities to participate in extensive professional development which has emphasised the place of assessment. Little research has been carried out about how teachers’ assessment practices have changed as a result of this and very few studies include the perspective of students. This study aimed to address this gap in research by establishing how four dynamic, committed teachers, in four different primary school settings, have changed their practices. It looked at how they currently view, understand and manage their assessment practices. The study included interviews with the school assessment leaders to establish the importance of the professional context in which the teachers work. Interview responses from the four teachers were compared with the responses of small groups of children from each teacher’s class to probe the related understandings and experiences of the students. The findings indicated that the teachers had made considerable shifts in their beliefs about assessment in the last six years. They attributed the reason for these changes to be largely the result of professional development and changes in the culture of the schools in which they work. The results of this study showed that the case study teachers had clear understandings of assessment theory, they prioritised formative assessment, they had become proactive in determining what assessment practices were worthwhile and they had reconstructed their classroom cultures to involve students in the assessment process. Each teacher had developed her own personalised assessment programme that included her own unique mix of strategies. They had successfully married their extensive use of formative strategies with the assessment requirements of their schools. They had become more critical assessors who were not prepared to undertake any assessment that they deemed lacked purpose. The case study teachers were enthusiastic about the changes they had made and felt they were better teachers now because of these changes. Similarly, the students who were interviewed for the study were also enthusiastic about and interested in their learning. They were able to talk about what assessment was for and able to explain the ways in which the assessment processes in their classrooms were helping them learn.