Pupils taking GCSEs and A-levels this summer will have their grades awarded by a combination of teacher assessment, class ranking and the past performance of their schools, the exam regulator for England has announced.

Ofqual, which oversees schools’ public examinations, laid out the new system to award grades after the government cancelled this summer’s exams because of the coronavirus crisis and the resulting school closures, which are likely to remain for the rest of the academic year.

The new system will affect around 1.5 million pupils studying for this year’s GCSEs, A-levels and AS-levels in England, as well as many in Wales. Details are still unclear for those taking BTec and vocational or technical qualifications at schools and colleges.

Experts have cautioned that relying on teacher assessments is likely to penalise students from disadvantaged backgrounds, according to Jo Grady, the secretary general of the University and College Union.

“Our primary concern is that disadvantaged students are the ones most likely to miss out. Research shows that they fare badly when it comes to predicted grades and they are less likely to be able to put life on hold and delay sitting exams, or have access to the tools required to navigate any appeals system,” Grady said.

Daisy Christodoulou, the director of education at the assessment organisation No More Marking, said Ofqual’s system was likely to lessen at least some potential sources of bias.

“We are in unprecedented times and given the impossibility of holding exams it is hard to see what else could have been done. Ofqual’s requirement for a grade and rank order seems like the best information they could require at the moment and will at least help to iron out inconsistencies between centres,” she said.

Sally Collier, the chief regulator of Ofqual, said: “We have worked closely with the teaching profession to ensure that what we are asking is both appropriate and manageable, so that everyone can have confidence in the approach.”

In a message to students, Collier said: “The grades you get this summer will look exactly the same as in previous years, and they will have equal status with universities, colleges and employers, to help you move forward in your lives.”

Hamid Patel, the chief executive of the Star Academies group, said Ofqual’s announcement was fair and involved a minimum of bureaucracy, but he raised concerns about pupils taking GCSEs a year early in year 10. Ofqual is consulting on whether they sit the exams next year instead of being awarded a grade for their work this year.

“Clearly we would have all wanted the examination season this summer to continue as planned,” he said. “However, that is not possible as we have a duty first and foremost to ensure the wellbeing and safety of pupils, families and staff, including saving lives.”

Under Ofqual’s system, schools will be asked to recommend a grade for pupils in each subject, and to “rank order” candidates within each grade, from the pupil the school is most confident about receiving that grade to the least. The assessments will be kept confidential and not shared with individual students.

Each candidate’s final grade will be assigned by the exam boards using a model under development by Ofqual, using the prior attainment of the year group at each school and college, each centre’s exam performance in recent years and the expected national outcomes for all pupils.

The regulator said schools would submit their assessments to the exam boards from 29 May, and that it hoped to publish the final grades on or before the usual mid-August results season.

Ofqual’s announcement left questions still to be answered, however, including how appeals against final grades will be conducted and when students will have an opportunity to “re-sit” their exams next year.

The regulator said it was still considering how to award grades for external candidates, those taking the exams without a formal affiliation, such as students being home-schooled.

Paul Whiteman, the general secretary of the National Association of Head Teachers, said the move was pragmatic and avoided extra burdens on schools.

“Of course this is not a seamless solution. Students will have been expecting to go through a very different process. However, their grades will now be determined by the professionals who know them best, professionals who are well-equipped to make these judgments, and we hope that gives students confidence that they are in safe hands,” he said.

Gavin Williamson, the education secretary for England, said: “Despite the difficult circumstances we are facing, this guidance provides assurance to students, parents and schools that grades awarded this summer will accurately reflect students’ abilities and will be as valid this year as any other.”