The headteacher of a school with around 1,000 pupils has told parents it will not reopen for at least a week because of concerns about dangerous concrete.
Scalby School, in Scarborough, North Yorkshire, is one of more than 100 schools across the country told by the government to take action following the discovery of lightweight concrete used in buildings.
In a letter to parents, headteacher Chris Robertson said measures had been taken to allow the school to operate as normal after reinforced autoclaved aerated concrete (RAAC) was identified last term.
But the Department for Education had changed its guidance, leading to "some unavoidable disruption to students' education".
Mr Robertson said: "Currently we believe significant parts of the school site are affected by the change in guidance. This also includes access routes around the school building. This is going to have a significant impact on the education provision we can offer in the short term."
He said the school, which was due to welcome pupils back on 5 September was trying to keep the impact on students "to an absolute minimum".
"However, I must inform you that school will not now reopen until Monday 11 September," he wrote.
"This will allow us time to reorganise the school curriculum, work with contractors to start work to reopen parts of the building and ensure that the school is fully risk assessed."
Teaching would then be likely to be "a mix of face to face and online home learning", he said.
RAAC is a lightweight building material used from the 1950s up to the mid-1990s, but now assessed to be at risk of collapse. It is believed to have a lifespan of around 30 years.
The government initially said more than 104 schools and colleges had been told to partially or fully close buildings just days before children were due to return to classes because of the issue with RAAC.
But schools minister Nick Gibb told ITV News there's "perhaps a few more" which could be affected.
He said the government had sent surveys to 22,500 schools in England and the "vast majority" did not have RAAC but "some" still have not returned their questionnaires and their buildings could contain the dangerous concrete.
In his letter, Mr Robertson said staff were still working through the implications of the issue at Scalby School.He told parents: "As soon we have concrete proposals in place as to what this looks like I will write to you and inform you."
He added: "I appreciate that the timing of this decision, shortly before the start of the autumn term, is far from ideal.
"This decision has been taken out of an abundance of caution to ensure pupil safety, and we will be doing all we can ensure that the impact on students is kept to a minimum."
North Yorkshire Council said no other schools in the county were affected.
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know.