Twenty years after the publication of "Inside the Black Box," the landmark review of formative classroom assessment, international education experts Christine Harrison and Margaret Heritage tackle assessment for learning (AfL) anew, with fresh insights gained from two decades of research, theory, and classroom practice. "The Power of Assessment for Learning: Twenty Years of Research and Practice in UK & US Classrooms" examines the practices and processes of formative assessment over time in both countries, evaluates the benefits accrued to teaching and learning, and considers future developments in growing and sustaining AfL practice. It features: (1) Key AfL ideas, approaches, and supports; (2) Vignettes of classroom practice that illustrate AfL in action in the U.K. and U.S.; and (3) Practice-based evidence to enrich understanding of AfL from both the teacher's and the student's perspective. Focused on student-centeredness and rich with classroom examples, this book is a 'sounding board' for educators to explore and reflect on their own AfL practices and beliefs. [Foreword written by Dylan Wiliam.]