There is an extensive structure of formal student assessment in England, Wales and Northern Ireland. Although the structures in each of these countries were similar when they were initially introduced two decades ago, they have increasingly diverged over the last decade. This national description outlines the development of statutory assessment from the Education Reform Act 1988 to reforms announced during this academic year, 2008/09. It provides an overview of the aims and organisation of the arrangements for statutory assessment in 2008/09 and looks at the use and impact of the results of such tests. It also provides information about selection tests at age 11 where these are still in use. In England, Wales and Northern Ireland, there is currently an emphasis on the use of "assessment for learning" (AfL). AfL is based on the idea that students will improve most if they understand the aim of their learning, where they are in relation to this aim and how they can achieve the aim (or close the gap in their knowledge). It is conducted during day-to-day classroom practice and takes place during learning. It also gives students an active role in the assessment process. Another form of testing undertaken in all parts of the United Kingdom is testing for international studies of student attainment, such as those organised by the OECD Programme for International Student Assessment (PISA), the International Association for the Evaluation of Educational Achievement (IEA) Trends in Mathematics and Science Study (TIMSS), and the IEA Progress in International Reading Literacy Study (PIRLS). This paper discusses the objectives, organization, and use of results of the national testing of pupils in the United Kingdom. (Contains 20 footnotes.)