In this new edition of his best-selling text, Brian Butterworth explains the very latest research in the science of dyscalculia in a clear, non-technical way. Crucially, he shows that dyscalculia is caused by a core deficit in the ability to accurately and swiftly represent the number of objects in a set, an ability that underpins learning arithmetic, and clearly differentiates dyscalculia from other forms of early mathematical learning difficulties. This new edition includes a review of the new evidence for effective intervention, examines new research on the role of memory, intelligence, and how they interact with the core deficit. With new chapters on number sense, the arithmetical brain, governmental changes around the world, and evaluations of new interventions, this invaluable text is fully supported with a wide selection of online useful resources and courses. Butterworth uniquely links research to pedagogical practice, to explain how science can be used for the identification