How the World’s Most Improved School Systems Keep Getting Better is a McKinsey & Company report that attempts to answer the question posed in its title through an examination of 20 education systems in action. These 20 school systems, which come from all parts of the world, have achieved significant, sustained, and widespread gains, as measured by national and international standards of assessment. The report builds on the 2007 McKinsey & Company report on the common attributes of excellent school systems titled How the World’s BestPerforming School Systems Come Out on Top. It includes in its appendix an explanation of their system selection criteria, as well as the database structure for the detailed evidence the researchers gathered to map the experiences of nearly 575 reform interventions made across the school systems. In addition to a quantitative analysis, the researchers interviewed more than 200 system leaders and their staff and visited all 20 systems to see them in action. In the current report, the authors sort out various education systems according to their starting point and progression, according to four performance stages: from poor to fair, fair to good, good to great, and great to excellence. In each case study of an improving education system, the authors argue that the system is led by astute leaders who are able to manipulate a small number of critical system parameters to create positive movement. However, the researchers are also able to point out the elements which are specific to the individual system and those which are of broader or universal relevance. The first section of the report is about ‘‘Intervention’’. According to the authors, every school system faces the challenge of deciding the interventions it should make in order to improve its performance. The authors contend that their research identifies common clusters of interventions that all improving systems carry out at each journey stage on the long path from poor to excellent. They argue that a