Accountability has always been deemed a necessity for schools to fulfill their purpose in society. Because of the nature of their operational core, this has for a long time been based on bureaucratic and professional accountability in most countries. In the second half of the 20th century, several countries have started implementing instruments of managerial accountability. While bureaucratic accountability means that accountability is focused on functionality and regularity, and professional accountability means that the profession itself defines standards and mechanisms of holding one another accountable, managerial accountability focuses on the effectiveness of schools based on externally defined standards instead. In many countries, this change of focus in the accountability system has entailed strengthening the managerial power of school leadership and introducing performance measurement through tests and inspection. This has shifted the power balance between teachers and schools on the one hand, and education authorities on the other. At the same time, it has created the opportunity for schools to use the new data for improvement, albeit with varying results. The fact that so many countries have adopted managerial accountability accordingly is not based on evidence about its positive effects, but on convergence in an international organizational field. However, comparisons of accountability systems in the United Stated, Germany, and Finland show that the adoption of this global strategy is dependent on how it fits with the local institutional norms in each country. While the United States have traditionally had a system of managerial accountability, the other two countries have only recently supplemented their systems with elements of managerial accountability, and the instruments are therefore adapted to each context.