This study looks at the impact that the National Certification of Educational Achievement (NCEA) has had on teacher collegiality in New Zealand. It is an exploratory study using an in case and cross case method, located in four secondary schools with a range of demographics. I was interested in gathering the information from teachers in three key roles: Assistant teacher, Head of Department and Principal's Nominee, finding out what their views were on the change that the NCEA has bought to their professional lives and the impact made on their collegiality. The literature reviewed shows there is an international appreciation of the value of collegiality in schools but there is a fragile nature of collegiality that challenges its strength. The complexity of school culture and the symbiotic relationship between it and collegiality contributes to challenge of the management and development in secondary schools. The findings showed the teachers in this study considered there to have been a deepening in collegiality as a result of increased sharing of material, professional communication through moderation and professional development, and a heightened respect for professional practice and understanding of personalities. There are threats from reduced socialisation, workload, loss of autonomy and the fragility of collegiality. These elements have created a shift in school culture. How teacher collegiality can best be supported using this assessment policy has been explored with features involving school organisation and increasing deep collegial activities such as collegial observation, marking, moderating and review being identified as beneficial.