Parents, pupils and teachers at two north Wales schools are having to make last minute arrangements after being told their sites are to close over concerns about dangerous concrete.
Extra precautions are taking place following structural worries about Reinforced Autoclaved Aerated Concrete (Raac) - a lightweight form of concrete which is much weaker.
The news was delivered on Monday just a day before the schools were due to return for the Autumn term, causing disruption to hundreds of families.
So why has this happened so late?
The Welsh Government is blaming the UK Government claiming it didn't share the latest evidence about risks relating to Raac until last night (Sunday 3rd September).
The Education Minister Jeremy Miles said he was still unaware of the full evidence the UK government has on the dangers of Raac in buildings.
"They've had this information for a long time and they hadn't disclosed it to the devolved governments until last night.
"It's time for governments to work together on this kind of issue, so I've asked the secretary of state to convene urgently the intergovernmental Racc working group."
He went on to say 'schools are safe' adding the closures are a 'precuationary measure' while more tests are carried out.
In a statement, a Welsh government spokesperson added: "It is hugely regrettable that the evidence that has apparently been developed over the summer has been withheld until the night before the first day back of term.
"It is also incomplete, leaving us without the full rationale for the Department of Education's sudden policy change towards the management of RAAC in schools."
What does the UK government have to say about these claims?
A spokesperson for the Department of Education said: "We have been working with the Welsh Government for several years and kept them informed as to our concerns about RAAC.
"We met with officials from the Welsh Government to discuss emerging evidence in June, before meeting to discuss our change in policy on Friday.
"We started our survey programme in 2022, which is much earlier than other nations and means we are in a strong position to understand the risks to the school estate."
Welsh Conservative Leader Andrew RT Davies, said: "Labour ministers in the Senedd can't pass the buck. They're in charge of schools in Wales, so building safety is their responsibility.
"Unlike in England, where decisive action was taken by the Conservative Government, Labour have sat on their hands in Wales and put pupils' safety at risk."
What is RAAC?
Reinforced Autoclaved Aerated Concrete (Raac) is a lightweight form of concrete.
The way that Raac is created makes it weaker than the normal building material.
There is no coarse aggregate - for example, gravel and crushed stones - in Raac, this is what gives concrete its strength.
Instead fine aggregate - such as sand and stone particles - is combined with chemicals to create gas bubbles, and heat to cure the compound.
This makes it relatively weak.
In some schools, roofs are constructed using Raac planks, which are long slim blocks of the material.
Professor Chris Goodier, a leading expert on RAAC at Lougborough University, previously explained the difference between RAAC and modern concrete to ITV News' Daniel Hewitt
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