This introductory chapter presents the key concepts discussed in the subsequent chapters of the book. The book is grounded in contemporary international policy contexts in which performance in the internationally competitive global market increasingly shapes education at a national level. In a policy climate in which evidence of pupil learning, and the best way to achieve such learning, become the essence of school accountability, any process that seems to offer gains in learning is likely to be hijacked by game-playing tactics. Feedback seems to have succumbed to such tactics and is increasingly precisely constructed and focused on nationally tested learning outcomes and levels. Despite its potential to be 'effective', it is clearly not effective for all pupils. Whether in the USA or UK, standards of learning do not rise in the same way for all pupils. Three distinctive conceptualisations of the learning gap are offered which look differently at influences on and approaches to framing the learning gap.