Laura Doel, director of NAHT Cymru, said: “The impact staff absence is having is widespread and showing no signs of letting up.  School leaders are stepping back into the classroom to cover classes and doubling up as lunchtime supervisors and caretakers just to keep their schools open.

“No-one is monitoring the impact staff absence is having on schools nationally, it’s completely hidden from public view. It’s recorded locally at local authority level but no-one is digging further and looking across Wales to find out what is really happening. Schools cannot continue in this way, staying open with supply staff if you can get them and the goodwill of the staff members that remain.

“Any hope of rolling out a successful new curriculum, developing a new qualifications system and trailing new Estyn inspection relations is dwindling by the day. Schools simply cannot keep on trying to cope.

“We aired our concern that the removal of so many mitigation measures in schools was a mistake at the start of September and continue to urge the Welsh government to review the situation.

“If the situation continues and no support is offered to schools, staff absence will result in school leaders being forced to close their schools.”