Teachers unions are warning Northamptonshire's schools will struggle to cope unless more Covid-19 tests are made available for staff and students.
Hundreds are being forced to self-isolate and unable to return to school after failing to book appointments at testing sites in the county.
And National Association of Schoolmasters Union of Women Teachers says its members are expressing "serious concerns" about the impact on schools and the situation is getting "increasingly out of control."
The NASUWT Executive member for Northamptonshire, Alan Hackett, said: "Risk assessments schools relied upon are predicated on access to Covid-19 testing and the capacity to effectively and appropriately isolate suspected and confirmed cases.
"Pupils sent home with symptoms are facing uncertainty about when or where they will be able to access a test. With the delay in testing, pupils and staff who are part of a ‘bubble’ within a school are not being isolated even where there are multiple suspected cases and/or where multiple pupils displaying symptoms have already been sent home.
"This is putting at risk the health and safety of others within the school and within the local community.
"Schools appear to be seeking to do their utmost to carry on. However, we have reports that schools are unable to cope with a situation that is becoming increasingly out of control.
"There is clearly a need for further advice to all school and academy employers reiterating the essential steps they must follow in these circumstances and where pupils or staff are unable to obtain a test."
So far, 11 schools in the county have confirmed coronavirus cases among students or staff forcing year groups to study at home while self-isolating.
County Public Health officials have so far refused to discuss the situation after being approached by this newspaper on multiple occasions.
Health Secretary Matt Hancock told the Commons yesterday the lack of capacity in testing labs could take weeks to fix.
Meanwhile, appointments at eight testing units in Northampton, Kettering, Corby, Wellingborough and Daventry are being limited to prioritise hospital and care home workers as the testing programme struggles to cope with recent spikes in demand.
That means many with Covid-19 symptoms are unable to get a test which could allow them to return to work or school.
We revealed yesterday how families are either being turned away from a test centre in Northampton for not having an appointment or had only earned a slot after hours of trying.
One mum said: "My daughter can't go back until she gets a test. She's missing out on her first week back at school.
"I was trying 11am yesterday. I finally got one at 8.30pm. I just sat there refreshing it again and again.
Another mum spoke to the Chron after she was turned away for not having an appointment.
She said: "I managed to book two appointments for my children — they offered me centres in Leicester and Kettering. I was prepared to go, absolutely.
"But when I went to put my car reg plate in and confirm it, it booted me out and I couldn't book it.
"I came down today just to try my luck. No one in the house can carry on until we get tested. I'll just have to keep trying."
Local MP Peter Bone wrote to the Health Secretary following a personal visit to the Wellingborough testing centre on Monday.