The gap in GCSE results between pupils who receive free school meals and those who do not has widened.
52% of pupils who were eligible for free school meals earned grades between A* and C in comparison to 79.3% for pupils who did not receive free school meals.
With respect to A* grades, pupils receiving free school meals also scored 11.5 percentage points lower than those who were not eligible.
David Evans, National Education Union (NEU) Cymru secretary, said that the results have shown that the pandemic has disproportionately affected those from poorer backgrounds.
He said: "Poverty has been an issue here. The pandemic hasn't hit people fairly.
"There will be children who haven't had the space to learn at home and who haven't had the resources to learn at home and will have to share resources and be in cramped spaces and that is a genuine unfairness we can't do anything about at this stage.
"It's not going to be a quick fix. We need to work with all the organisations to see what can be done to repair that situation, to make sure in the future learners are on a fairer level playing field.
"This has definitely been a factor in widening the gap and the task now will be for Welsh government to see what can be done."