What factors in the classroom environment and instructional practice exert the most significant influence on student achievement? John Hattie, a professor of education, synthesizes data from over 800 meta-analyses to quantify the relative impact of various educational interventions. By calculating effect sizes, the author establishes a framework for identifying which teaching strategies, school structures, and student attributes correlate with the highest gains in learning outcomes.

Experts and educators frequently cite this work as a foundational text for evidence-based practice in modern schooling. Readers often note the high density of statistical data, which requires careful navigation to fully grasp the implications for classroom implementation.