The purpose of this article is to present a case of national achievement assessment at the primary level within a formative approach. Many countries experience an increasing obligation to attach high stakes to national assessments, which results in greater pressure on teachers and schools. The author's view is that this kind of approach is misdirected if, at the same time, teachers do not have the opportunity to learn how to enhance their teaching. The information generated by national assessments should contribute to such an opportunity. This article presents a brief presentation of the Uruguayan education system. It provides a brief history of national assessment and its purposes. It explains the main features of the assessment system and addresses the key issue of disseminating the outcomes. This article describes how the author tries to transform quantitative results into research and in-service teacher training in order to improve teaching and learning in disadvantaged schools. Some evidence about the impact of this assessment approach is presented. (Contains 7 tables, 4 figures and 8 notes.)