New Zealand is a relatively high performing country according to international assessments. It has transited the journey to develop a strong student assessment system. This paper describes this journey, highlighting drivers that helped shaped the assessment system, and drawing lessons for other countries aiming to undertake this journey. This case study shows that New Zealand revamped its assessment system in the context of broader education and curricular reforms. A new vision of assessment for learning was realized in national large scale assessment, secondary school examinations, and classroom assessment activities. Key drivers that allowed these reforms to take place were strong leadership at all levels of the education system, clear vision and agreed upon principles, stakeholders who were assessment literate, and regulations that gave discretion to the schools to self monitor their performance.