School buildings in Northern Ireland are being assessed due to concerns about collapse-prone reinforced autoclaved aerated concrete (Raac).
Thousands of pupils in England face disruption at the start of term this week following an order to fully or partially close 104 schools over safety concerns about Raac, which was widely used from the 1950s to mid-1990s.
The UK Department for Education has so far refused to say which schools are affected.
Education Secretary Gillian Keegan has vowed to publish a list of the schools affected by the concrete crisis this week.
She sought to defend the Conservatives' record when challenged over cuts to school rebuilding.
It was put to her on BBC Radio 4's Today programme that, while senior officials recommended 300-400 schools be rebuilt every year, the government initially funded 100 a year and Rishi Sunak cut that to 50 a year when he was chancellor, years after ministers were warned about the risks of Raac.
She said: "I've just announced 239 school rebuilding projects", but could not indicate how many a year, saying only "as soon as possible".
She said the Department for Education is going "over and above" what it needs to do, stressing that "responsible bodies" are ultimately responsible for the buildings.
"We've delivered much better value for money, much more schools have been rebuilt, much more schools are going to be rebuilt, we've got a grip of Raac," she said.
Schools in Scotland and Wales are also being assessed for Raac.
The Scottish government has said it is present in 35 schools, but that none poses an "immediate risk" to pupil safety.
The Welsh government said councils and colleges have not reported any presence of Raac.
British Prime Minister Rishi Sunak defended the timing of the announcement over school closures.
He said: "New information came to light relatively recently and it's important that once it had, that the government acted on it as swiftly as possible.
"Of course I know the timing is frustrating, but I want to give people a sense of the scale of what we are grappling with here: there are around 22,000 schools in England and the important thing to know is that we expect that 95% of those schools won't be impacted by this."
If, as Mr Sunak said, 5% of schools are impacted, that would mean more than 1,100 are affected.
Questions also remain over the extent to which the problem has been complicated by the co-existence of asbestos in schools and other public buildings.
Chancellor Jeremy Hunt promised yesterday to "spend what it takes" to make classrooms safe, but Treasury sources later said there were no plans for additional funding.
He moved on the weekend to reassure parents that an "exhaustive process" has been carried out to identify any unsafe buildings, amid accusations ministers failed to act quickly enough to mitigate risks raised in 2018.
He said Ms Keegan had "acted immediately" after new information came to light over the summer about the potential risk Raac, a lightweight material used up to the mid-1990s.
Ms Keegan has promised the crisis will not lead to a "return to the dark days of lockdown", despite the new guidance advising schools to use pandemic-style remote learning as a last resort if they are unable to hold face-to-face lessons.
Writing in The Sun On Sunday, she said there was "no choice" other than closures after a "handful of cases" where Raac had failed.
Remote learning for children unable to access face-to-face lessons should last "days, not weeks", the government has said, but ministers have refused to indicate exactly when the overarching disruption might ease.
In the mean time, education leaders have been encouraged to use community centres, an "empty local office building" or other schools for the "first few weeks" while structural supports are installed to mitigate the risk of collapse.
