One of the most important issues accompanying the publication of the main results of the well-known Programme for International Student Assessment (PISA) is the classification of countries according to student attainment. However, this ranking does not take into account some highly relevant factors, such as the different resource endowments of each education system or the heterogeneous context in which schools operate. This study aims to provide a fuller picture of education system operation worldwide by assessing the managerial efficiency of secondary schools in a cross-country framework. To do this, we use data from OECD countries participating in PISA 2015 and apply a robust nonparametric approach that accounts for the fact that schools were operating under heterogeneous conditions before the efficiency measures of performance were estimated. Our results suggest that the consideration of both school resources and environmental factors significantly modifies the country ranking based solely on student results.