Obtaining parental consent has been the biggest challenge for schools in the rollout of asymptomatic testing for pupils for the full return, a new poll has found.
More than half of respondents said this had been a difficulty, according to the survey by the Association for School and College Leaders (ASCL).
Over the first two weeks of term, secondary school and college pupils are being asked to take three Covid-19 tests on site and one at home, after which they will then be sent home-testing kits to do twice-weekly.
Schools and colleges have been allowed to invite some pupils onsite for their first Covid tests this week to help manage the rollout.
"It is worrying that the biggest problem emerging is the difficulty in obtaining parental consent for Covid-19 tests,” ASCL general secretary Geoff Barton said.
"This is most likely to be simply a matter of oversight with some parents not returning forms and we would urge them to do so.”
Mr Barton encouraged parents to speak to the school if they have any concerns over testing.
He added: "These tests are voluntary but the more they are used, the better the chance of detecting asymptomatic cases."
While ASCL found 52 per cent of leaders surveyed said they had faced problems with getting parental consent for testing, more than 40 per cent said they had struggled to find the space for testing stations and get enough staff to run them.
All pupils are expected to be back in class by 15 March - one week after all students are to be allowed back onsite.
The full return comes around two months after schools moved online for all but key worker and vulnerable children amid the coronavirus pandemic.
The ASCL poll of 934 headteachers of secondary schools and colleges in England found around three quarters said they will need to phase the return of students during the course of next week.
Meanwhile, seven per cent of school leaders in the survey - carried out by email on Thursday - said they expected the staggered return of pupils to continue into a second week.
On Friday, the Royal Statistical Society’s Covid-19 Taskforce called for transparency on the rollout of lateral flow tests in secondary schools, saying pupils’ results from the twice-weekly asymptomatic tests should be made public.
A Department for Education (DfE) spokesperson said: "Our guidance is clear that secondary schools and colleges can stagger the return of their students over the first week to help them offer rapid testing in a safe and orderly way, but all students should be back no later than Monday 15 March.”
"We know the vast majority of schools are working towards getting students back as soon as possible.”
The spokesperson added: “Wherever it becomes clear that is not the case, our regional schools commissioner teams work closely with councils and trusts to make sure schools follow our guidance in the best interests of their students."
Additional reporting by Press Association