The UK is below average in an international comparison of social mobility within school systems, according to analysis published last week by the Organisation for Economic Cooperation and Development (OECD).
It shows that Shanghai in China, South Korea and Finland are among top performers in results and equity, but across the OECD there is a strong link between social disadvantage and low achievement in school.
The UK is successful in results, but weaker in terms of fairness.
This latest OECD study, based on analysis of fair opportunities for pupils, compares the reading skills of teenagers against the levels of social equity, using data from the 2009 Programme for International Student Assessment (Pisa) tests.
"On average across OECD countries, disadvantaged students are twice as likely to be among the poorest performers in reading compared to advantaged students," the report says.
But the study adds that there is nothing inevitable about this connection between social background and achievement.
At the top end of the international spectrum, Shanghai, Finland, South Korea, Canada, Japan, Hong Kong and the Netherlands are among a select group of school systems with very high results and high levels of fairness, where pupils can succeed regardless of background.
Russia, Spain, Croatia and the Czech Republic are relatively strong on equal opportunities, but have low performance.
Bulgaria, Turkey and Kyrgyzstan perform poorly on both equity and results.
The UK belongs to a group of countries, including France, Germany and the United States, that are above average for results, but have lower levels of equity.
Andreas Schleicher, the OECD's special adviser on education, said a long-term characteristic of the UK's education system has been social division - with a polarisation between the results of rich and poor pupils.
But although the UK remains less equal than the OECD average, there has been an improvement.