From the start of term next month pupils will no longer need to wear masks, socially distance, stay in bubbles or self-isolate if in contact with a positive case.
Headteachers are calling for high quality ventilation systems to help reduce the spread of the virus.
Department for education guidance says classrooms should be kept “well ventilated” but school leaders said more support is needed.
Some schools, such as the London Enterprise Academy in Tower Hamlets, which is in a former office block, has no windows that can open.
Paul Whiteman, general secretary of school leaders’ union NAHT, said: “Good ventilation is now widely accepted as being key to preventing the spread of Covid. Schools therefore need more than the glib advice to ‘open a window’, which isn’t possible for some, or sustainable as we move into autumn and the winter months.”
He added: “The government must urgently invest the time and money necessary to make sure classrooms are adequately ventilated.
“Given that it has removed the majority of the measures that were in place to reduce Covid transmission in schools, the least it can do is to take seriously the ones that remain, or we will continue to see major disruption to children’s education.”
Carbon dioxide monitoring equipment is being rolled out in Scotland to help identify poorly ventilated areas in schools. Measuring the accumulation of carbon dioxide levels is an indicator of how much fresh air is circulating.
Thirty schools in Bradford are taking part in trials using air purifiers and ultraviolet light to combat Covid-19, while the Department for Education is taking part in a pilot project to measure CO2 levels in classrooms. But it is not known when this will be implemented and on what scale.
The schemes have been criticised for being “too little, too late”. Dr Patrick Roach, general secretary of union NASUWT, said CO2 monitors should be in place in every school as part of the Covid safety response.
He added: “A commitment from ministers to a fund to provide enhanced ventilation, monitoring and support with air filtration would be an extremely positive move.”
Geoff Barton, general secretary of the Association of School and College Leaders, said: “We are calling on ministers to provide funding for high-quality ventilation systems in schools and colleges to help reduce the risk of coronavirus transmission.”
A government spokeswoman said: “We want to ensure schools are both safe and comfortable for students and staff – and good ventilation has consistently been part of government guidance. We are working to identify cost-effective ways to reduce transmission in communities.”