Class remains a national obsession in England. Its education system is notorious for the gap between its wealthiest public schools and toughest comprehensives.
But is it true that "performance still has a stronger link to socio- economic background than is the case in the world's best systems"? The table (below) appears to back this up. It shows England and most of the 20 comparison countries chosen by consultants McKinsey.
The figures show the difference between average maths test marks for 13-year-olds from homes with more than 200 books and those with fewer than 10.
On this crude measure, based on figures from the Trends in International Mathematics and Science Study in 2003, England has the biggest gap.
But dig into more recent statistics and the picture becomes less clear.
The Programme for International Student Assessment (PISA) tested 400,000 students around the world in 2006 and rated each against a complex measure of economic, social and cultural status.
The rankings results remained roughly the same. But the UK fell back to joint third most affected, tied with Belgium, with the US second and New Zealand first.
More curious was what happened when PISA looked at the difference which social background made to schools' results rather than individual pupils. A school with an intake one step up the PISA-developed social scale over another could expect to get 133 more test points in Japan, 123 in the Netherlands, 114 in Germany, and 102 in Germany, but only 71 in the UK.
The class gap
Saudi Arabia - 29
Bahrain - 40
Hong Kong - 41
Jordan - 58
Canada - 62
Belgium - 63
Japan - 71
Netherlands - 75
Australia - 77
New Zealand - 88
Singapore - 88
US - 92
England - 93.