Plaid Cymru has accused Labour and the Liberal Democrats of "staggering hypocrisy" for attacking A-level downgrading in England, after thousands of students also had their grades lowered in Wales.
The parties criticised the UK Government for downgrading the results of nearly 40 per cent of A-level pupils in England.
Exams were cancelled across the UK due to the coronavirus lockdown, with students instead being given A-level grades estimated by their teachers.
But Welsh A-level students had their results downgraded from teacher estimations by more than 42 per cent, leaving many frustrated and prompting calls for an urgent review.
Plaid Cymru leader Adam Price has called on the Welsh Government to reassess its approach, accusing Labour and the Liberal Democrats of "political game playing" over students' futures.
Mr Price said: "The hypocrisy from UK Labour and Liberal Democrat parties in their vocal outcry of UK Government’s 'botched grading system' and of 'robbing' these students of their future while their Welsh Government counterparts commit the same gross error is staggering.
"Young people have suffered enough this year already. What we shouldn't be doing is adding further to that anxiety and distress by seeing their future life chances determined by an algorithm.
"Pupils who were awarded lesser grades than the teacher assessments in A level and AS exams should be upgraded to the teacher assessment grades."
In England, Education Secretary Gavin Williamson announced late on Tuesday that students would be able to use grades from mock exams to progress to university, college courses and employment.
Labour leader Sir Keir Starmer described the last-minute government approach as a "complete fiasco", calling for urgent changes to be carried out.
"To have an 11th-hour decision that’s caused widespread chaos amongst teachers I have been speaking to, families and young people – it smacks of incompetence," he said.
The Education Minister for Wales also made a last minute change prior to results day, confirming that no A-level student would be awarded a grade lower than their previous AS grade.
But unions, teachers and students have criticised the "devastating" impact of standardised grades.
Mike Hedges, Labour Member of the Senedd for Swansea East, echoed a similar message to Adam Price, saying the results had been dealt with "appallingly".
"It's people's lives we're talking about, not an algorithm, not about trying to make thing statistically correct," he said.
"These are real people whose lives are being disrupted."
He has called for all A-level grades to be reassessed.
Kirsty Williams, the only Liberal Democrat in the Labour Welsh Government, dismissed claims that results day had been "chaotic".
"The decision to cancel the exams in the first place was one that was not taken lightly, but clearly was the right one to make. I'm confident that today we have fair and robust qualifications for our students," she said.
First Minister Mark Drakeford said: “Research by one of the authors, CEPEO Deputy Director Dr Gill Wyness (UCL Institute of Education), earlier this year showed that only 16% of university applicants were correctly predicted across their best three A-levels, when comparing teachers’ predictions to students’ actual grades. Of the rest, 75% were overpredicted and just 8% underpredicted.”
Mr Starmer insisted his criticism referred to England not providing reassurance with AS-levels, paying for an appeal and keeping people waiting for results far longer than in Wales. The First Minister added their position is "very different".
He said: "England, where they don't have AS-levels; England where you have to pay for an appeal; England where people will be kept waiting for longer for results than they have here in Wales."
"The big picture is we have more students achieving, more students achieving at the very top end of the scale, and a record number of people from Wales accepted into university."
He added that students with anomalies in their results would be able to access a free appeals process.
The Welsh Liberal Democrats said no student has been downgraded.
"Kirsty Williams introduced a no-detriment policy to ensure that every student is guaranteed at least the grade achieved in their AS level last year.
"This is only possible because we have kept AS levels in Wales, which is a better indication of a student’s abilities. Even Gavin Williamson has admitted that he would like the AS system that we have in Wales.”
The Welsh Government has been asked to comment.