Children from the most deprived areas of England are falling further behind in school compared to more affluent pupils, say the Conservatives.
Exam results show the social divide
Shadow Schools Secretary Michael Gove highlighted figures showing a widening of the social gap in achievement.
There is a 43 percentage point gap in the proportions of wealthy and deprived pupils achieving five good GCSEs including English and maths in 2007.
In 2006, this gap in favour of the wealthiest was 28 percentage points.
This social divide in exam results shows "the education system is letting down the poorest," says Mr Gove.
The figures are based on comparisons of the GCSE results of pupils from the 10% most affluent areas and the 10% most deprived.
The growing lead reflects an accelerating improvement in the results of children from better-off families - with 68% of these pupils now reaching the benchmark of five good GCSEs including English and maths, up from 57% in 2006.
Meanwhile, the results of the least well-off pupils have slipped back - down from 29% to 25% reaching this GCSE benchmark.
The government figures show how the link between home background and achievement stubbornly persists throughout children's years in school.
At the age of seven, there is a 20 percentage point gap between the proportion of most and least affluent pupils who have reached the expected standard for reading - 93% to 73%.
By the age of 11, this gap has widened to 23 percentage points for English.
In secondary school, these latest figures for GCSE level show that the gap between richest and poorest grows even further to 43%.
When the school population is divided into 10 bands of affluence and deprivation, the level of achievement rises in precise step with increased wealth in every subject and at every level.
The figures also show that this most deprived group are a major factor in the drop-out rate at the age of 16.
In primary school, those living in these 10% most deprived areas are the biggest single social group. In terms of those studying beyond the age of 16, they are the smallest group, with numbers shrinking by about 90%, and their average A-level point score is the lowest.
These figures reflect the attainment gap using another poverty indicator - free-school meals.
In 11 year olds reaching the expected literacy levels, there is a 21 percentage point gap between pupils who qualify for free-school meals and wealthier pupils who do not qualify.
A spokesman for the Department for Children, Schools and Families said that "closing the attainment gap continues to be a top priority".
"We have invested more than £21bn in child care and the early years since 1997, so that poor children get better chances in early life.
"One to one tuition and personalised support will help every single child achieve the best of their ability at school and we have ensured that in future all young people will stay on in education or training to 18 and beyond."