The discussion in Ireland around post-primary teachers (catering for students aged between 12- and 18-years of age) being responsible for assessing their own students’ work continues. The Junior Cycle Reform (covering the first three years of post-primary education) is concerned with making fundamental changes in approaches to learning, teaching, curriculum and assessment, with school-based assessment as an important element of the reform. This presentation maps and discusses the area of mediation of assessment policy in a changing and contested assessment environment in the Republic of Ireland. To do this, the presentation tells the story of assessment in junior cycle. The story evolves as one in which government policy was intent on promoting a teacher-lead, learning-oriented assessment practice which was actively resisted by the Irish post-primary teacher unions through their insistence that a centralized, externally-conducted assessment at the earlier stages of post-primary education was preferable to school-based, teacher-led assessments.