The index is built to be internationally comparable (see the PISA 2012 Technical Report, OECD, 2014a). Students are considered socio-economically advantaged if they are among the 25% of students with the highest ESCS in their country or economy, socioeconomically disadvantaged students are those among the 25% of students with the lowest ESCS. Schools are defined as socio-economically advantaged (disadvantaged) if the average ESCS of students in the school is statistically significantly above (below) that of the average school. These patterns reflect, in part, the inherent advantages in resources that relatively high socio-economic status provides.