In this paper we develop a measure of rank mobility between socio-economic background and academic achievements. We then use PISA 2012 international test scores in Math to estimate both the resilience and the social mobility of the different school systems in the OECD countries. Using the social mobility concept, we revisit the education equity and efficiency tradeoff. We show that the social mobility is positively correlated to the education performance (i.e., average test score) and negatively correlated to the education inequality (i.e., variance of test scores). We also show that social mobility is inversely related to segregation dissimilarity index. In the second part of the paper, we estimate what accounts for the differences in the school levels of social mobility using a cross-country regression with random effects. The covariates are related to the school composition (average socio-economic index, social mix, ethnical background, truancy,...) and the school policy (grade repetition, ability grouping, teaching differentiation, school practices for behavioral problems and low achievers, extra-curricular activities, soft skill teaching, academics standards , budget autonomy, human resource policy, accountability policy...).