The university admissions system should be “overhauled” to reduce inaccurate predictions of A-level grades which can unfairly disadvantage comprehensive school pupils, a report suggests.

A paper, from the UCL Institute of Education, says university applications should be delayed until students have received their A-level results to help remove potential inequalities.

Researchers said they could only predict a quarter of pupils’ best three A-levels correctly – even after removing any opportunity for bias.

High-achieving students in non-selective state schools are also more likely to be under-predicted at A-level compared to their grammar and private school peers, the study suggests.

The findings come ahead of A-levels results day on Thursday, where students will find out whether they have met the requirements for higher education.

Moving towards a post-qualification admissions (PQA) system should be considered, rather than university offers based on predicted grades, as getting predictions right is a “near-impossible task”, researchers have said.

Academics – from UCL Centre for Education Policy and Equalising Opportunities and Oxford Brookes Business School – studied data from 238,898 pupils’ GCSE performance to see whether they could accurately predict their subsequent A-level results.

Among high achievers, the researchers found 23% of comprehensive school pupils were under-predicted by two or more grades compared to just 11% of grammar and private school pupils.

Co-author Professor Lindsey Macmillan said: “This research raises the question of why we use predicted grades at such a crucial part of our education system.

“This isn’t teachers’ fault – it’s a near-impossible task. Most worryingly there are implications for equity, as pupils in comprehensives are harder to predict.”

Co-author Dr Gill Wyness said: “We definitely don’t think teacher predictions should be replaced by computer predictions – this research serves to highlight the difficulty faced by teachers, and provides further evidence that the UK’s predicted grades system should be re-examined.”

In February, the Office for Students (OfS) launched a review into university admissions – including the use and accuracy of predicted grades.

Possible reforms to the sector could include saving university offers until after a student has received their A-level results, or delaying the application process until after results day.

A poll, carried out by the University and College Union (UCU), suggests many school, college and university leaders support exploring a PQA system.

Three in five – of the 128 respondents to the online survey – felt the current system was not fit for purpose, according to UCU and the National Education Opportunities Network (NEON) report.

Jo Grady, UCU general secretary, said: “Thousands of A-level students are receiving their results this week, but the current university admissions system, based on inaccurately predicted results, means students from disadvantaged backgrounds are more likely to lose out.

“Allowing students to apply after they receive their results would help level the playing field for disadvantaged students, remove the problems associated with unconditional offers and end the chaotic clearing scramble.”

Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), said: “Teachers do their very best to predict A-level grades for students who are applying for university, but the system is far from being ideal, and it is incredibly difficult to get it spot on with every student.

“It really is high time that we looked again at a system whereby students apply to university after they have received their grades.

“This has been made more pressing by the habit of universities giving students unconditional offers which leads to some being demotivated in their A-levels and other important qualifications. The whole thing is a bit of a mess.”