The schools minister has said he trusts "the judgement of teachers" amid warnings that the government's new grading system could undermine the value of qualifications.
The government is expected to task schools with determining pupils' grades in lieu of exams this year, because of disruption caused by coronavirus.
Education Secretary Gavin Williamson is to set out further details of the plan in the Commons later on Thursday.
But some experts have warned that the approach could lead to inconsistent outcomes across schools and even see top grades devalued.
The Education Policy Institute (EPI) think-tank warned the plans could cause "extremely high grade inflation".
But ministers are keen to avoid a repeat of last year's fiasco when grades were effectively tweaked by an algorithm based on past results, causing widespread perceived unfairness.
Natalie Perera, chief executive of the Education Policy Institute (Epi) think tank, said: "Without timely and detailed guidance for schools on how this year's grades should be benchmarked against previous years, and with classroom assessments only being optional, there is a significant risk that schools will take very different approaches to grading.
"This could result in large numbers of pupils appealing their grades this year or extremely high grade inflation, which could be of little value to colleges, universities, employers and young people themselves."
Schools minister Nick Gibb said there would be checks in place "at the school level and at the exam boards level to make sure that we do get consistency" across the country.
Others were broadly welcoming of the approach and said it was the best option available in the circumstances.
Leora Cruddas, chief executive of the Confederation of School Trusts, said: "There is a reasonable consensus that teacher judgment will need to be both supported, scaffolded and quality assured.
"This is because although the pandemic has had a damaging impact, we still want assessment outcomes this year to reflect something objective."
Paul Whiteman, general secretary of the school leaders' union Naht, said the plans "appear to chart a path which avoids the awful chaos of last year".
He said: "This set of decisions is, however, only the starting point. It is now down to the awarding bodies to provide the detail which schools and colleges need to implement the process.
"Although earlier results for students seeking to start university could be beneficial, cramming GCSE results into the same week will place unnecessary pressure on to the system."
Mary Bousted, joint general secretary of the National Education Union, said the approach was "likely the least worst option available".
But she added: "However, there are still question marks over how it is expected that the extra work necessary to facilitate grading will be dealt with."
Speaking ahead of the Commons announcement, schools minister Nick Gibb told BBC Radio 4's Today programme: "We trust the judgment of teachers. They're the people who know their pupils best.
"On top of that, there are all these checks both at the school level and at the exam boards level to make sure that we do get consistency and there is a range of evidence that backs up the judgment of that teacher when they send the grades to the exam board.
"There are all kinds of detailed guidance from the exam board to make sure that teachers across the country are applying their judgment in a consistent and fair way."
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