Academic selection is the process of selecting students based on academic ability and then providing divergent educational routes depending on the results of the selection. Drawing on international evidence, this book provides detailed discussions on the influence of early-age academic selection on educational effectiveness and equity. Demonstrating its widespread implementation across England, Northern Ireland, Germany, the United States, and China, the book provides a comprehensive evaluation of academic selection, considering policy implications, practical applications, and societal controversies. Through a systematic analysis of empirical studies, the book critically evaluates the potential impacts of academic selection on educational effectiveness and equity, exploring whether expanding or replacing it with a non-selective system would lead to more effective and equitable outcomes. With significant implications for improving educational effectiveness and equity, this book will be invaluable to students and researchers of education policy and sociology of education, as well as to policymakers in countries with existing academic selection systems or considering their implementation.