Despite the UK’s leading role in public management reform, and decades of continuous change, little has been learned of the final outcomes. Our understandings of the impacts are fragmentary. A theoretical explanation has three elements. The first comprises the inherent technical and methodological difficulties of evaluating complex major organisational change over time. The second identifies reasons why it is unlikely that most executive politicians will invest energy in systematic evaluation. The third emphases specific institutional features of organisational reform in UK central government. Changes can be made and remade with (comparative) ease – tempting elites constantly to reinvent.