A senior headteacher has warned of the potential for a “lost generation” of school children due to the coronavirus pandemic as huge numbers continue to miss classes.

The academic year is coming to a close against a backdrop of half-empty schools as children and teachers are forced into self-isolation amid rising Covid rates.

Figures on Tuesday showed more than a million children were out of school last week.

That was no surprise to Richard Sheriff, executive headteacher of the Red Kite Learning Trust, who said roughly 20% to 40% of students were off in the 13 schools he oversees in West and North Yorkshire.

“After the optimism in May when we returned, we felt really back to normal,” he told the PA news agency.

“This new wave of the virus has just put us right back and I think it’s made it a rather sad end to a very difficult year.”

Schools across the country, which have already been closed for long periods since last March, are seeing mass student absences because of Covid.

Mr Sheriff said causes for that include students who have tested positive, those who are isolating due to being a close contact of someone who has, or those whose class or year group bubbles have been affected.

It has also been reported that some parents are keeping their children home from school in the later weeks of term to avoid missing summer holidays due to isolation.

Mr Sheriff, who is also president of the Association of School and College Leaders, fears the build-up of absences and closures could create a lasting effect for some children.

“Before this pandemic, we were worried about the gaps in our society – the attainment achievement gaps and progress gaps between children in our poorest communities, and those in our most well-to-do communities,” he said.

“Those gaps have undoubtedly, undoubtedly widened during this.

“Pulling that gap back is going to be extraordinarily hard, and we could see the spectre of a lost generation of children.”

Mr Sheriff said some children have been relatively unaffected, if they were lucky enough to have family members or guardians overseeing their home schooling, or help from tutors.

But he added: “For many children we serve, who live in the poorest of our communities where parental support is not there for them in that way, they have got a very, very, very steep mountain to climb in front of them to get back to anything like parity with more privileged peers.

“And I really don’t think what the Government has done so far has gone any way to bringing that gradient down, and giving them a fair chance to climb the mountain.”

Sir Kevan Collins, the education catch-up commissioner, quit his role over the Government’s proposal of a £1.4 billion fund to help children recover missed lessons – he had proposed a £15 billion recovery package.

Mr Sheriff said it was “bitterly disappointing” to see Sir Kevan’s plan “turned away to such an extent”.

He added: “Maybe we can’t have all of it but to have what we’ve had from it, which is a lot of recycled money and ambiguity about how and where that money’s going, it’s not good enough to close the gap that will have got even wider during these last few weeks.”

He suggested he is broadly sympathetic to the difficulties of responding to a pandemic, and that “mistakes” from those in power are inevitable when working in such exceptional circumstance.

But he said: “I think what makes it hard to forgive those mistakes is the lack of what appears to be honesty and openness from the most senior levels of Government.

“And that makes it very hard for us working in the system, when our leaders don’t lead us in a way that we think is either ethical or effective, to forgive them for the mistakes they make.

“There’s a feeling that there’s a disconnect between the Government and the people it’s responsible for giving orders to, and I think we need to close that and win back trust, and that trust, I think, has evaporated during the course of this pandemic.

“I think that’s the most worrying thing going forward.”