Pupils hoping to appeal against the results of their exams this summer will find it harder to get their marks changed following a crackdown announced by the exam regulator.
Ofqual will harden its stance on appeals to prevent some students getting a "second bite of the cherry" if they are unsatisfied with their initial mark at GCSE and A-level.
It follows an increase in the number of reviews requested by pupils and schools in 2015, with some 460,000 challenges lodged last summer.
Under the new system, a change to a mark will only occur if it is found a "clear marking error" has been made.
It is claimed that this will lead to a "fairer" system, after it was discovered that some original marks were being overturned despite being "perfectly appropriate".
Ofqual's executive director for general qualifications Julie Swan said: "It is not fair to allow some students to have a second bite of the cherry by giving them a higher mark on review, when the first mark was perfectly appropriate.
"This undermines the hard work and professionalism of markers, most of whom are teachers themselves.
"These changes will mean a level playing field for all students and help to improve public confidence in the marking system."
Asked if she felt this would add to the pressures of exams for students, she said: "Not as a result of these changes, no."
The decision follows a consultation with schools' groups, subject associations, teachers and students.
More than 90,000 grade changes took place as a result of challenges lodged at GCSE, AS and A-level in the summer of 2015.
Of this total, only 639 qualifications shifted more than two grade boundaries.
In recent years there has been a marked rise in the number of reviews requested, growing from around 190,000 challenges in 2010 to more than 414,000 in 2014.
Ms Swan added that the surge in appeals reflected the "huge pressure on schools" to ensure their students get the best grades possible.
Other changes announced by the regulator include reviewers being monitored for consistency and the way being opened for exam boards to allow students to appeal to them directly, rather than through their school.
Ofqual's chief regulator Sally Collier said: "Professional judgement needs to be exercised, not overwritten.
"Our decisions will define a new era in fairness for all students, teachers and schools."