'this work is highly relevant to the proliferation of accountability measures worldwide' James Scheurich and Douglas Foley In many countries, the lives of teachers and children are increasingly dominated by programmes of national testing of mathematics and other subjects. In England, the majority of the items in such tests have set mathematical tasks in every day situations such as 'shopping'. This requires children to make decisions about whether to use or not their own every day knowledge and experience in their problem-solving. Some children are likely to have a better 'feel for this game' than others. Assessing Children's Mathematical Knowledge draws on the analysis of national curriculum test data from more than 600 children of 10-11 and 13-14 years of age, as well as in-depth interviews with 250 of these as they attempt to solve test problems, in order to explore the nature of the difficulties children experience with 'realistic' items. The book shows, by comparing test and interview data, that many children, as a consequence of their confusion over the requirements of 'realistic' test items, fail in tests to demonstrate mathematical knowledge and understanding that they actually possess. The book also explores whether this problem of invalid measurement is equally spread across children from different social backgrounds, and across the sexes. The book will be of interest to academics and teachers studying for advanced degrees in mathematics education, sociology of education and educational assessment.