Ideally, school systems provide high-quality educational opportunities for all students, irrespective of the students’ backgrounds. Students from socio-economically advantaged families and those from disadvantaged families should be equally likely to succeed in school. That is the ideal, anyway. In most countries, the reality looks a lot different. PISA results have consistently shown that socio-economic disadvantage is linked to poor performance in school. In fact, on average across OECD countries, disadvantaged students are twice as likely to be among the poorest performers in reading compared to advantaged students. On average, a socio-economically advantaged student scores 88 points higher on the PISA reading test than a socio-economically disadvantaged student, a difference that is equivalent to more than two years of schooling.

Yet the fact that countries and economies vary in the degree to which learning outcomes are linked to socio-economic background demonstrates that social background is not destiny, and that policy and practice can make a difference. Moreover, countries can pursue equitable learning outcomes while also moving towards high student performance. In the PISA 2009 survey, many of the countries and economies with the greatest equity in student outcomes are also top performers. Students in Canada, Estonia, Finland, Hong Kong-China, Iceland, Korea, Liechtenstein and Norway score above the OECD average in reading, and the difference in performance between advantaged and disadvantaged students is less than 70 score points. Other countries and economies also achieve equitable learning outcomes, but their students do not perform as well.

Azerbaijan, Indonesia, Jordan, Macao-China, Qatar, Serbia, Thailand and Tunisia are as equitable as the preceding group of countries, but their students score below the OECD average in reading. The difference in reading performance between advantaged and disadvantaged students is highest – more than 100 score points – in Argentina, Austria, Belgium, Bulgaria, Dubai (UAE), France, Germany, Hungary, Israel, Luxembourg, New Zealand, Panama, Peru, the United States and Uruguay.
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Other countries and economies, namely Canada, the Czech Republic, Hong Kong-China, Mexico and the United States, also improved their equity levels without a concurrent improvement in overall performance.

http://www.oecd.org/pisa/pisainfocus/pisa%20in%20focus%20n25%20%28eng%29--FINAL.pdf