Bright poor boys are around two-and-a-half years behind their rich, clever male classmates in reading, a study has suggested.
It reveals that high-achieving boys from disadvantaged backgrounds are more likely to perform poorly on international tests than those in other nations.
The report, commissioned by the Sutton Trust, warns that action must be taken to ensure that schools are supporting bright students so they do not lose out on top university places and good jobs.
The study analysed the 2009 scores of 15-year-olds taking part in the Organisation for Economic Co-operation and Development (OECD) international PISA reading tests.
It found that bright English boys from the poorest families lagged 30 months - two-and-a-half years - behind their high-achieving male classmates from the richest backgrounds. This gap was bigger in England than in every other developed nation apart from Scotland.
In countries such as Canada, Denmark, Germany and Finland, this gap was 15 months or less, the study found. It added that among clever girls, the reading gap between those from the richest and poorest homes was two years and four months.
The researchers also looked at the gap in reading skills between children of all abilities. The findings showed that in general, the poorest teenagers in England lagged two years and four months behind their richest classmates in reading. This put England 23rd out of 32 countries who took part in the tests, ahead of countries including the USA and France, but behind others including Norway, Chile and Slovenia.
Sutton Trust chairman Sir Peter Lampl said: "This matters for two important reasons. First, it is clearly economically inefficient not to tap into talent wherever it exists. By not stretching our most able students from all backgrounds, we are not only failing them, we are reducing our ability to compete globally. Second, such under-achievement perpetuates those inequalities which make it so hard for bright children to move up in society."
The study, by Dr John Jerrim of the Institute of Education, comes weeks after Ofsted warned that tens of thousands of clever children were being let down by England's state secondary schools. A culture of low expectations in many schools meant that bright pupils were not being stretched and were failing to gain top grades at GCSE, according to a report published by the inspectorate.
A Department for Education spokeswoman said: "This report, based on data from 2009, demonstrates the appalling attainment gap that has been a feature of our education system for far too long. Our reforms will ensure every child has the chance of a decent education."