If we want our students to thrive in the impossibly complex, unpredictable world of the 21st century, we must concentrate on increasing educational achievement by increasing the quality of the teachers in our schools. In this book Dylan Wiliam argues that quality of teachers is the single most important factor in the education system. He outlines the many possible ways in which we could seek to develop the practice of serving teachers and concludes that of these, formative assessment has the biggest impact on student outcomes. He looks at some of the popular initiatives that aim to increase student achievement, such as learning styles, and presents research that shows formative assessment practices have a much greater impact on educational achievement than most other reforms. Formative assessment functions to the extent that evidence about student achievement is elicited, interpreted and used by teachers and learners to make decisions about the next steps in instruction that are likely to be better than the decisions they would have made in the absence of that evidence. The five key strategies of formative assessment that Wiliam outlines are: Clarifying, sharing and understanding learning intentions and criteria for success; Engineering effective classroom discussions, activities and learning tasks that elicit evidence of learning; Providing feedback that moves learners forward; Activating learners instructional resources for one another; Activating learners as the owners of their learning. Wiliam presents a summary of the research evidence that shows the impact of each of the above strategies, and offers over fifty practical techniques that teachers can use to incorporate the strategies into their classroom practice.