comparisons are made between pisa and pisa the last time mathematics was assessed in depth to account for the extent to which the observed relationships are influenced by the level of economic development of countries and economies the comparison of school systems discussed in this chapter also considers national income per capita per capita gdp among all countries and economies that participated in pisa of the performance variation among students is observed at the system level is observed at the school level and is observed at the student level the crossnational analyses provide an overview of how systemlevel attributes and major organisational arrangements relate to student performance and equity in school systems