For the first time, professors will have detailed information that allows them to compare the quality of schools before candidates are offered places.

A new application form, sent to schools last week, asks what proportion of pupils at the school achieved three A grades at A-level and how many went on to university. It is the first time a university has asked for so much detail about the success of the school.

The aim is to help professors differentiate between pupils who achieved top grades at strong state schools, where they had lots of academic support, small class sizes and training on how to apply, and those who reached the same level with no such advantage.

It is part of a wider drive among universities to select 'high potential' pupils from less affluent backgrounds.

In making the changes, academics at Oxford have rejected controversial plans, announced earlier this year, to check the family backgrounds of undergraduates, by asking if their parents went to university.

Mike Nicholson, Oxford's director of undergraduate admissions, argued that the question provided information that was 'unverifiable' and unhelpful in choosing between students. 'If they say "yes", it could be that they are the 51st generation at university, or one parent may have an Open University degree,' he said. 'You cannot differentiate between those students with a "yes" or a "no". We want the educational context rather than the personal one.'

The new application form includes guidance telling referees to state whether pupils received additional support during their application, whether there was a high turnover of teachers and the percentage of pupils who received free school meals - information that is accepted as a guideline to the educational status of schools.

Nicholson said Oxford had a 'conscious obligation' to seek out the best students regardless of background, and the new information on schooling would be one factor that could help them. 'Potential is very difficult to measure,' he said. 'But we are keen not to just look at [students'] existing performance but how they could do over three years. A student who is in an environment with a lot of support will be well prepared. Where a student has less support, we need to factor that in.'

Nicholson pointed out that Oxford receives almost 14,000 applications each year, all from straight-A students, for 3,500 places. 'What I would like to see is that we get all the information we need to help us make those difficult calls between applicants.'

The Oxford plan comes days after new figures revealed that Britain's top universities were falling short of the benchmarks for recruiting both state school pupils and those from poorer backgrounds. Only six of the 20 members of the Russell Group, which represents the country's most elite universities, met their targets.

Oxford recruited 53.7 per cent of its candidates from the state sector, compared with a benchmark of 72.9 per cent. Meanwhile, 5.9 per cent of students came from deprived neighbourhoods, falling short of the target of 8.7 per cent.

However, critics warned that universities should not use 'social engineering' to try to manipulate the figures. Some fear that Oxford will use the details about educational background to discriminate against pupils at the best schools.

'I am all for widening participation,' said Pat Langham, president of the Girls' Schools Association. 'But I think that all educational information that can be used for statistical purposes has to be viewed with suspicion.' She said there was nothing wrong if Oxford used the information only when looking at individual candidates, but she feared that if it were used to fill quotas it could lead to students from high-performing schools being discriminated against.

It is already a fear circulating among some parents who have paid huge amounts to put their children through the independent sector. The mother of one boy who has just completed his GCSEs at a private school in Manchester admitted she was considering moving him to the state sector for his A-levels: 'He really wants to study law at Oxford. I think that will improve his chances.'

But others said the worries were unfounded. 'We are talking about a university that still gives 50 per cent of places to pupils from public schools; that is hardly discriminating,' said Sam Freedman, head of research at the Independent Schools Council.