Head teachers said work was either late, shoddy or did not happen
Cornwall Council is having to spend millions of pounds patching up schools after the collapse of a major contract.
Their upkeep passed into private hands in 2001, but an investigation by BBC Inside Out has revealed some are now in a worse state of repair than before.
Problems include fire doors not fitting properly, a landslide in a playground, rotten windows and a rusty gas pipe.
A total of 28 schools are affected and the council has estimated the bill to put things right will be about £10m.
In 2001, Cornwall County Council signed a 25-year, £74m deal with a consortium called NewSchools Cornwall to refurbish and maintain the schools.
It was funded by the government's Private Finance Initiative (PFI), which is a way of getting the private sector to invest in public projects.
Instead of Cornwall Council having to raise the funds for the work on the money markets, NewSchools Cornwall would secure the financing instead and do the job in return for regular payments from the council.
At the start, classrooms were added and refurbished, but ongoing maintenance problems began to surface, with head teachers saying work was either done late, shoddily or not at all.
Charles Boney, chair of governors at Trewidland Primary School, near Liskeard, said the management problems had been a big distraction.
"We don't become governors in order to become crisis managers but that's what's happened," he said.
"There's been a huge number of meetings and detail that we've had to pay attention to when we ought to be focussing on keeping up the standards in a very good school like this."
After seven years of complaints to the council and NewSchools Cornwall, the government intervened and the deal was terminated.
NewSchools Cornwall went into administration owing its various backers more than £40m.
Inside Out South West has seen a confidential report, commissioned by the council, which concluded the authority's management of the contract was poor.
It was supposed to penalise NewSchools Cornwall if it did not do the job properly, but, according to the report, this did not happen correctly.
NewSchools Cornwall has in the past publicly apologised for "inexcusable deficiencies " and said its costings "proved over-optimistic".
In a statement to the BBC, a spokesman for the consortium's private investors stressed the project was tendered under EU procurement rules and only went ahead after the council took professional advice over the projected costs.
Cornwall Council says improvements are being done as quickly as possible
But Professor Allyson Pollock, of Edinburgh University, an expert on the private finance initiative, said the problems in Cornwall were part of a "catastrophic failure" of similar PFI schemes, involving other consortia, across the country.
She said Cornwall's experience should prompt a major inquiry.
Cornwall Council told the BBC the project had been one of the first of its kind in England and "very little guidance was available...to local authorities".
It said improvements were carried out as quickly as possible after the independent review into its contract management.
The council also said it had stepped in to ensure the schools continued to receive essential maintenance.
In the meantime, legal negotiations are under way because even though the deal went wrong, Cornwall Council will have to pay compensation to NewSchools Cornwall and its financial backers.
That amount could run into millions.
Inside Out South West will be broadcast on BBC1 on Monday 15 February at 1930 GMT.