GCSE and A Level students in England have been assured that their final grades will not fall below their mock exam grades.
Following a U-turn from the Scottish government over exam results, the UK government has promised a s-called "triple lock" on grades for students in England.
This means that students will awarded the highest result out of their estimated grades, mock exam grades, and an optional written exam in autumn. This change means that students can appeal their grade if they get an estimated grade lower than the result of their mock exam.
They will have to appeal through their school, with the terms to be decided by exam watchdog, Ofqual.
'Mock exams don't conform to the same standards'
Geoff Barton, leader of the ASCL head teacher's union, told the BBC the move "beggars belief", pointing out that schools carry out mock exams in very different ways, meaning they are not consistent enough to determine GCSE and A Level results.
"The government doesn't appear to understand how mock exams work. They aren't a set of exams which all conform to the same standards. The clue is in the name 'mock'," said Mr Barton.
Scotland's 'postcode lottery'
The move comes in the wake of an apology and policy change from the Scottish government, which had previously seen exam grades lowered by a moderating system which critics called a "postcode lottery", as it linked results with the past performance of a pupil's school.
The system was accused of discriminating against young people in deprived areas, where school performance may be worse. Now, the results will be based on predicted grades given by teachers.
'An extra safety net'
For English A Level students getting their results on 13 August, mock exams marked before the lockdown will now form a crucial part of deciding their results.
England's schools minister, Nick Gibb, told BBC Breakfast that the ability of these students to appeal on the basis of mock results is "an extra safety net for a small group of pupils."
He rejected concerns about confusion and told the show he would "apologise to nobody for finding solutions - even at the eleventh hour" to stop students being unfairly disadvantaged.