Parents should be aware that children can still be exposed to asbestos in schools, a union has warned.
Many teachers do not know whether their school contains the substance - which can cause a slow-developing cancer caused mesothelioma.
Recent figures obtained through freedom of information requests suggest that around 86% of school building contain asbestos, according to the National Union of Teachers (NUT) with those built between 1945 and 1975 most likely to be affected.
A small-scale poll conducted by the union found that 44% of members questioned said they do not know if their school or college contains asbestos - often found in ceiling and floor tiles, or window and door frames, while 46% said they had been told that it does and about 10% said they had been told that it did not.
One teacher said the first they knew about the substance in their classroom was when a caretaker came in with a pot and paintbrush and said he was sealing the asbestos panels.
Another said: "Someone drilled a hole in [the asbestos] to put a clock up."
Figures suggest that between 200 and 300 former schoolchildren die of mesothelioma each year, along with rising number of teachers, NUT deputy general secretary Kevin Courtney said.
He added that 22 teachers died from the disease in 2012, up from three in 1980.
Sarah Lyons, the NUT's lead on asbestos, said that questions over asbestos in schools should be asked, particularly because children are more vulnerable as they have more life ahead of them.
"Mesothelioma is a cancer that develops over a long period of time, 30 to 60 years, so the younger you are when you're exposed, the more at risk you are."
Asked if parents should ask their schools about the issue, she agreed that they should.
"As a union we are equally concerned for children as we are for teachers and support staff, but the dangers for children are more acute because they've got more life ahead of them.
Ms Lyons added that the issue has always been a concern, but added: "T he asbestos that's in our schools now is getting older and older, so it's deteriorating and if it's in a poor condition then it's in a more dangerous state."
The poll also found that 20% of teachers were aware that children are more at risk than adults, due to the long latency period for developing mesothelioma.
:: The NUT poll questioned 201 members in March.