Pupils are being taught in schools that are damp, have mould, or are simply not big enough, according to a survey of teachers.
It suggests that schools have had to take measures such as increasing class sizes and setting up temporary classrooms to cope with rising pupil numbers, while current buildings are beginning to crumble, or becoming unsuitable for staff and students.
The poll has been conducted by the NASUWT teaching union, which meets for its annual conference in Birmingham this weekend.
The research comes just weeks after official figures showed that secondary schools in England are facing a boom in pupils, with numbers set to rise by more than 654,000 by 2026.
More than a third of the 1,200 NASUWT members polled rated the physical condition of the buildings they work in as poor, with a further 36 per cent describing them as adequate, and the rest saying they are good or very good.
Seven in 10 suggested that there were signs of leaks, damp or mould around their school, while just over half said the same about their classrooms.
One teacher told the union: “My classroom has thick black mould growing up the walls, the paint is peeling and the room smells very damp.”
Another said: “The school is too small for the number of pupils. It is damp and cold - I have to have a dehumidifier running constantly in my room.
“There are patches of damp in the ceiling and the whole building needs painting inside and out. There is asbestos in the roof space.”
Just 36 per cent agreed that classrooms and teaching spaces were large enough for the number of staff and pupils using them, while 30 per cent agreed that communal spaces such as dining areas and halls were big enough.
A total of 70 per cent agreed that their school’s outdoor space was large enough for the number of pupils that use it.
But 42 per cent said that there were an adequate number of toilets and sinks for staff and pupils, with 47 per cent agreeing that toilet facilities were in good condition.
A total of 48 per cent said that the number of pupils at their school had significantly increased in the last five years, with 16 per cent saying numbers had decreased and the rest said they had stayed roughly the same.
Of those that said pupil numbers have risen, 20 per cent said the school had been extended, rebuilt or moved to a new site to cope with demand, while 72 per cent said class sizes had become larger, and 21 per cent said temporary classrooms had been created, or other areas of the school used.
One teacher told the NASUWT that their classroom was “very small” with little storage space.
“Last year some children in my class of 30 had to crawl under tables to get to their seats,” the union member said.
NASUWT general secretary Chris Keates said: “Our children and young people deserve a learning environment which enhances their experience and provides them with the fit-for-purpose spaces and facilities they need and deserve.”
Forecasts published by the government show that around one in six secondaries (16.2 per cent) and more than a fifth (22.8 per cent) of primaries are full, or in excess of capacity.
The increase in pupils numbers is largely due to a spike in the birth rate in the early 2000s.
