Ms Somerville said pupils unhappy with the grades they are awarded by their teachers can appeal against them directly to the Scottish Qualifications Authority (SQA) for free for the first time.
However, she said appeals could see results downgraded as well as upgraded – despite calls from children’s rights experts for a “no-detriment” approach to be taken after a year in which the Covid pandemic has seen schools closed for months on end, and pupils left to home-school remotely.
Ms Somerville also said that grounds for appeal would only be on "disagreement with the centre’s [school’s] quality assured academic judgement, contested administrative or procedural error within SQA or the centre; and appeals related to the Equality Act, including assessment arrangements”.
“It is right in these exceptional times that there is a broad mechanism to appeal for those who consider they have not received the right result, to review it, and which is free at the point of use,” she said.
“Education stakeholders have been clear that demonstrated attainment is a key principle in ensuring credibility and fairness of the qualifications, and so appeal decisions will be evidence-based and symmetric, meaning that grades can move down as well as move up, or stay the same depending on the review of the evidence.”
She added: “I recognise that some stakeholders are not supportive of this position and would seek an approach where grades cannot go down. While I am fully sympathetic to the position of learners this year, awards must, ultimately, be based on the actual attainment of pupils.
“That means that the subject specialist looking at an appeal must be able to give their true judgement on a pupil’s attainment, moving the grade in line with the evidence. In this way, the appeals system will be fair, consistent and credible.
“Without symmetry, there would not be a full and fair review of the evidence.”
However, the process was immediately branded by opposition parties as “worse” than last year as it does not take into account the impact of Covid on young people.
Scottish Greens education spokesman Ross Greer said the SQA had “lost the confidence of Parliament” and Ms Somerville’s statement had underlined that fact.
“The lack of a no-detriment approach to appeals means young people will be taking a perverse gamble,” he said.
“Schools will submit the strongest evidence they have in support of the initial grade. Why would they have stronger evidence, suitable for an appeal, but which they chose not to submit in the first place?
“It seems the risk of downgrading is increased by an appeals process reliant purely on limited and likely weaker evidence, rather than on the professional judgement of teachers. It appears personal circumstances such as immediate family bereavement due to Covid won’t even be taken into account.”
Scottish Conservatives education spokesman Oliver Mundell said both the government and the SQA had “betrayed” young people and “put them in an even worse position than pupils who were affected last year”.
He said: "The fiasco of last year’s exams was bad enough for Scotland’s young people, but shamefully the SNP have put this year’s pupils in an even worse position. That is simply unforgivable.
“First they told them exams were cancelled again, but they have completely failed to address their concerns about sitting exams in all, but name.
“Putting in an appeals process to try and rectify this long after deadlines have been missed just doesn’t cut it. The SQA is completely unfit for purpose and must be replaced by a body that will be trusted by parents, pupils and teachers.
“Our young people have suffered huge disruption due to the pandemic. It is completely unacceptable that the SNP Government have failed to be on their side and are now greatly running the risk of harming their future prospects yet again.”
Scottish Labour education spokesperson Michael Marra said Ms Somerville had “failed to produce a credible and coherent appeals process”.
He said: “Eight months, six promises and two deadlines later, pupils, parents and teachers are still in the dark on key questions.
“At the centre of this are individual pupils left on their own to decide whether to contest the grades given to them. To do so would be to question their school, the SQA and the government that set the process. They would risk being downgraded if they speak up.
“No allowance will be given for personal circumstances faced by pupils.
"We know that the most disadvantaged young people have been worst affected. They are also those most likely to require the support of their school rather than disputing the school’s conclusions.
“No new evidence will be allowed. Essentially centres will be reviewing the same set of assessments. If young people feel that their ability is not reflected in these grades, they have no recourse whatsoever.
“It is astonishing that we find ourselves here. There is little comfort for pupils, parents and teachers in this process.”
Later, Mr Greer said he understood the National Qualifications Group – established by the government after last year’s exams debacle – had not signed off on the appeals process.
Ben McKendrick, chief executive of the Scottish Youth Parliament, which was on the group, tweeted his agreement with the MSP, suggesting the SQA had “designed an appeals process with the express aim of discouraging as many appeals as possible”.
However, the process was supported by EIS general secretary Larry Flanagan, whose teaching union was on the group, especially as the “responsibility for handling appeals will rest with the SQA rather than schools”.
He said: “There is a quite phenomenal amount of work being undertaken across schools by teaching staff to ensure that young people are appropriately accredited for their learning.
"The three-month lockdown and associated remote learning certainly concertinaed the time available for student production of evidence, but ultimately it is that evidence which allows teachers to exercise professional judgement in determining provisional results.
"Unlike high-stake exams, the evidence does not need to be produced in a one-off event and crucially, the professional judgment of teachers will not be challenged by the SQA – this was a critical point which the EIS successfully argued for as part of the ACM model.
“For many students, however, the key issue around grades is access to the next stage of their learning and more needs to be done to ensure that universities, colleges and indeed employers recognise the difficult year it has been and ensure that progression is not stymied for the want of a particular grade.”
Ms Somerville, who took over as education secretary in Nicola Sturgeon's Cabinet reshuffle two weeks ago, also told MSPs there would be more support for senior pupils’ mental health, with letters to be sent to every learner taking national qualifications “to outline support available and to provide links to online resources and helpline numbers”.
She said: “I can reassure the chamber that everything is being done has been done to ensure that the hard work of learners is recognised fairly at a time that will naturally be an anxious and stressful one for many learners and their families."
However Scottish Liberal Democrat education spokesperson Beatrice Wishart said the “stress and uncertainty” over assessments should ensure reform of the SQA.
“There are no excuses left,” she said.
“The education secretary says this is a naturally stressful time. But the mismanagement of this year's exams has increased stress levels, and pupils need extra support to help with that extra anxiety."
Ms Somerville also revealed the delayed OECD review into the Curriculum for Excellence would be published on June 21.