This book is about research- and evidence-informed educational improvement. It synthesises and reframes the distinct schools of thought within the Educational Effectiveness and Improvement (EEI) fields for a renewed research and professional education agenda. At the book's heart is a problem: that educational improvement is often short-lived, rarely achieved at scale and, as some prominent researchers have argued, mostly illusory. The chapters describe and critique this divided field and reviews, synthesises and reframes the combined knowledge base. Building on this acknowledge of division, the book looks with scepticism, pragmatism and optimism towards the future for solutions in evidence-informed improvement.