An estimated 700,000 children are being taught in unsafe or ageing school buildings in England that need major repairs, according to a report.
The National Audit Office (NAO) says the Department for Education (DfE) has, since 2021, assessed the risk of injury or death from a school building collapse as "very likely and critical".
But the risks have not been addressed because of years of underfunding.
The DfE says it has been "significantly investing in transforming schools".
An official said "nothing is more important" than safety at school - and the department had allocated more than £15bn since 2015 to keep schools safe and operational.
But the NAO, the UK's independent public spending watchdog, said the deteriorating condition of school buildings was damaging pupil attainment and teacher retention.
Mother-of-two Carla Ashman, from Sheffield, was struck in the face by a 15ft (4.5m) piece of fascia board, covered in nails, that fell from the school building as she waited to collect her children.
She was left with a black eye, repetitive headaches and tinnitus, which still affects her several months later - but says it could have been much worse.
