We relate students' math scores in the OECD-PISA test to school characteristics. The average math score for Italian students has been increasing in 2009. The determinants of this growth are analyzed by the Oaxaca-Blinder decomposition, that is particularly useful in comparing groups. The progress in educational attainments shows a different composition between northern and southern schools. In the North-Center regions, improvements are explained by school endowments, while in the South they are also driven by external factors that are not explained by the estimated model and are linked to improvements in students' attitude to education leading to a more favorable disciplinary climate. The regional gap decreases but does not disappear.