In line with international trends, assessment policies and practices have increased in importance in New Zealand over the last two decades. The focus in this article is on examining the contested nature of the development of an assessment culture in New Zealand--one that meets the needs of the government by providing information on school accountability and yet maintains the autonomy of schools to continue school-based decision-making. The article begins by providing background to the New Zealand context and a brief description of current policies. The main emphasis, however, is on three companion themes in the development of assessment policy--assessment and improvement, assessment and accountability, and assessment and sustainability. These themes were drawn from an analysis of key documents and aligned with a conceptual framework drawn from the schooling effectiveness literature to provide a lens to examine the past, present and possible future of assessment policy and practice in New Zealand. (Contains 7 notes and 1 figure.)