The Covid-19 testing chaos has proved a "huge problem" for 20 per cent of headteachers, who say they are "struggling" to keep their schools open as a result, Tes can reveal.
And a quarter of heads say problems with testing capacity have forced them to send at least one bubble home, according to new findings.
The views were collected as part of a wider Tes survey of 10,000 school teachers and staff.
Exclusive: One in seven teachers 'on the brink'
Asked "what impact are Covid-19 testing capacity problems having on staff and pupil absence at your school, if any?", one in five (20 per cent) of heads said: "It's a huge problem – we're struggling to keep the school open".
And one in four headteachers (26 per cent) answered: "It's a problem – we've had to send at least one bubble home as a result".
One primary head reported that "a normal two-day recuperation from a virus is now taking at least a week out of school".
"Staff and children have had to take more days off than they really needed as they couldn't get a test for a day or so, then waiting longer for results," they said.
And a secondary head said, while they hadn't sent a bubble home, "staff and parents are panicking and so are staying off with cold symptoms and demanding a test".
Many heads reported issues relating to reduced staff capacity, which had been sparked by delays in accessing tests and subsequent results.
One primary head said they had waited up to five days for staff to be tested, with attempts to cover classes proving "very chaotic" due to a lack of funds for supply teachers.
And another said they were themselves "covering classes and lunchtime duty due to absent staff".
An independent school head said: "It is the staff we have problems with, being at home for days because they can't get tests. I am doing the job of about four people daily to ensure the work is done."
And a primary head added: "We are rapidly using up resources for cover staff – if current pace continues, resources will be gone in matter of weeks and if no staff, no money to cover, [then] closure only option."
A government spokesperson said: "The vast majority of schools are open, with more than 7.2 million pupils estimated to be attending schools last week, gaining all the benefits of being in the classroom.
"Only a small minority of pupils are currently self-isolating and there is remote education provision in place for the short time they are unable to attend school.
"Testing capacity is the highest it has been, and anyone with coronavirus symptoms should book a test. The home testing kits supplied to schools can be used to help pupils and teachers who have symptoms but subsequently test negative, and are not close contacts of confirmed cases, to get back to work as soon as they feel well enough."