Assessment is a planned, collaborative activity with enormous potential and impact in relation to students’ and teachers’ experiences and lives. Whether at the level of a teacher planning next week’s work for a class, a parent seeking additional resources for a child with a learning difficulty, a student contemplating future educational or employment opportunities and directions or a regional education administrator seeking more funds for a curriculum innovation, assessment processes and outcomes matter. At all levels, attention to detail in the planning of assessment increases the likelihood that the effort will be worthwhile. Accordingly, national and international examinations and assessments such as GCSE exams and TIMSS are planned in detail well in advance. The work of teachers and schools is also characterised by increased attention to the extent to which appropriate provision is made for assessment in the school and individual teacher planning. Changing curriculum and new understanding of the role of assessment for learners and education systems mean that assessment will continually evolve.