This highly detailed study maps four decades of evolution of the concept of what constitutes effective school leadership‎.‎ It analyses the theoretical background to these developments and advocates the utility of thinking of a ‎'‎lean‎'‎ form of school leadership that is comparable to the concept of ‎'‎meta‎-control‎'‎‎.‎ A wide‎-ranging survey of the empirical research literature on leadership effects includes the presentation of results from earlier meta‎-analyses as well as a new meta‎-analysis on some 25 studies carried out between 2005 and 2010‎.‎ This survey demonstrates that older reviews and meta‎-analyses were predominantly based on so‎-called ‎'‎direct effect‎'‎ studies‎,‎ while more recent studies have tried to quantify the indirect effects of leadership‎,‎ mediated by other school variables‎.‎ While acknowledging the relatively small total effect of leadership on student outcomes‎,‎ the study does identify promising intermediary factors which‎,‎ stimulated by specific leadership behaviours‎,‎ impact on student performance‎.‎ The book ends by drawing out wider implications for educational practice and policy‎,‎ presented under headings such as ‎'‎schools need leadership‎'‎‎,‎ ‎'‎the toolkit of the school leader as a meta‎-controller‎'‎‎,‎ ‎'‎the special case of turning around failing schools‎'‎ and ‎'‎efficiency of school leadership‎'‎‎.‎ In passing‎,‎ the authors make several suggestions about potentially fruitful next steps in researching the effects of school leadership‎.‎