One teacher recently put their foot through a floor, according to a letter from Taverham Junior in Norfolk.
Head teacher Paul Stanley said it was "particularly galling" when money was being spent building new free schools.
Norfolk County Council said a report into Taverham's classrooms was being compiled, but had yet to be completed.
Mr Stanley said the classrooms had been at Taverham since the 1990s.
He said: "Children's learning is suffering, despite the excellence of the teaching, and they're having to live in completely sub-standard accommodation.
"We're quite happy being a local education authority school, but it is frustrating that there is money for other sorts of schools and local authorities are paying-off debts of schools that are becoming academies [out of local authority control].
"If there are schools with worse mobiles, I'd really like to see them."
A statement from the county council, the local education authority, said it was aware of the school's concerns over classrooms.
"After commissioning a report into their condition, [the council] is in touch with the school on the issue.
"All this in the context of limited funding for a remaining stock of aging mobiles.
"In the case of Taverham that process has started but is not yet complete - it is hoped a recommendation will be made to elected members of the council during the latter half of the autumn term."
The council said decisions on prioritising replacements for mobile classrooms had to consider which schools were in areas of population growth and whether better use could be made of existing permanent buildings on site.
A school has apologised to parents for the fact pupils are still being taught in mobile classrooms dating from the 1970s that should have been temporary.