Comprehensive school pupils should be allowed into universities on the back of lower GCSE and A-level grades than students from grammars and fee-paying private schools, according to new research.

A study commissioned by the Department for Education concludes that students from comprehensives with equivalent GCSE and A-level grades outperformed their more expensively educated peers at university.

Claire Crawford of Warwick University and the Institute for Fiscal Studies, the author of the report, said: "If you have in front of you a student from a state school and one from a private school with the same A-level grades, on average – and I should emphasise it is on average – it does appear that the student from the state school background or less effective school will go on to do better given the grades that they are entering with."

An independent school-educated student was 10% less likely to get a first or a 2:1 degree than a student educated at a comprehensive when they had the same A-level results and were studying the same subject at similar universities.

Crawford's research suggested that Oxford, Cambridge and other universities "may wish to consider lowering their entry requirements for pupils from non-selective or low-value-added state schools". But she was careful not to propose any specific difference in grade requirements.

Traditionally, Russell Group universities, such as Cambridge and Manchester, have insisted that A-level grade offers should remain the same for all applicants, regardless of school background.

Crawford added that the fact that "there are these systematic differences" in student performance means that "one thing that could be done is for universities to recognise that in the offers they are making to students… I'm definitely not saying everybody should do it, universities need to make their own decisions."

The research also found that comprehensive pupils with equivalent grades were less likely to drop out, failing to complete their degrees.

Crawford's study comes after research by the Higher Education Funding Council for England found that pupils from non-selective state schools outperformed their independent-school peers with the same A-level grades at university. It used a wider data set from the national pupil database of students who sat GCSEs between 2001 and 2008 and then followed their university career.

The study also finds that the bulk of university access campaigns, aimed at boosting the comprehensive school intake into some of Britain's best universities, - appear to be misdirected, and that more effort could instead be put into improving GCSE results and subject choices to widen participation.

University access schemes "targeted at students beyond the end of compulsory education are unlikely to be able to eliminate the differences in [higher education] participation that we observe between pupils from different types of schools", it says.

"This valuable research confirms the importance of students getting good advice on their subject choices at school," said James Turner, director of programmes at the Sutton Trust, which campaigns on the need to widen university participation.

"It also shows there is an 'achievement against the odds' effect – students getting to university in spite of attending a poorer school are more likely to do well once they get there."

Dr Wendy Piatt, director general of the Russell Group said: "Candidates' academic success is already considered in a broader context, and admissions tutors are skilled at assessing applicants individually and holistically to identify real talent and potential. The bottom line is we want to give places to the pupils with the qualifications, potential and determination to succeed.

"Admission to university is and should be based on merit, and any decisions about admissions must also maintain high academic standards."

In the report Crawford concluded it should be "of particular concern to policymakers interested in widening participation in higher education" if pupils from certain backgrounds were less likely to go to top universities, especially if those same students "outperform those from elsewhere once they are at university, even after accounting for their qualifications, subjects and grades on entry".