More than 1,000 clusters and outbreaks of coronavirus have taken place in educational settings since schools reopened in September, documents suggest.

Children aged 12-16 played a “significantly higher role” in introducing infection into households in the period after schools reopened their doors to all students, Government scientists have said.

The document, released by the Scientific Advisory Group for Emergencies (Sage), said there is no direct evidence that transmission within schools plays a “significant contributory role” in driving increased rates of infection among children.

But it adds “neither is there direct evidence to suggest otherwise”.

Public Health England (PHE) indicates there have been more than 1,000 instances when there have been two or more positive cases of Covid-19 in educational settings since schools reopened, it says.

The document, dated November 4 and published on Friday, suggests that secondary school pupils played a higher role in introducing infection into households as the prevalence of infection in children aged 12-16 increased between September and October.

But the difference is less marked for younger children, the document says.

The role of schools in community transmission “cannot be easily considered in isolation from wider measures”, the paper adds, as potential increases may emerge because opening schools enables other mixing to occur – such as parents being able to go to work, or socialising after dropping off children.

Sage has said there is low risk to children of suffering severe clinical disease from Covid-19 but there are “significant educational, developmental and mental health harms” to children from schools being closed.

It adds there is some evidence that epidemic growth restarted before the reopening of schools.

It comes as schools, colleges, nurseries and universities remain open during England’s month-long lockdown – which began on November 5.

Education unions attended a Department for Education (DfE) meeting, alongside PHE representatives, on Thursday to discuss data on transmission in schools.

Last week, all students and teachers in secondary schools and colleges in England were told to wear face coverings when moving around the premises under Government guidance.

Paul Whiteman, general secretary of school leaders’ union NAHT, said: “We remain particularly concerned about the spread of the virus amongst older pupils and in secondary schools, especially given that we know that the prevalence of the virus has risen significantly since schools re-opened fully.

“There are also worrying signs that older pupils could be playing a role in spreading the virus amongst family members, and this must be watched very closely.

“Overall, it remains the case that all education staff are being asked to remain on the front line and it is incumbent upon the Government to do more to ensure that all pupils and staff are kept safe.

“Routine testing and priority access to seasonal flu jabs are just two examples of how they could do this.”

Dr Mary Bousted, joint general secretary of the National Education Union, said: “We call on the Government to play a much more active role to suppress the transmission of Covid-19 within schools.”

“The situation is untenable and widespread disruption will continue unless the Government takes steps to get coronavirus under control in schools,” she added.

A Department for Education spokesman said: “The chief and deputy chief medical officers have been clear the balance of evidence is firmly in favour of schools remaining open, and have highlighted the damage caused by not being in education to children’s learning, development and mental health.

“Children are at very low risk from the virus, and staff are not at higher risk than those working in other sectors.

“We have strengthened the already rigorous measures schools are following to reduce transmission of the virus, including requiring face coverings in all secondary schools in communal areas outside classrooms.”