Another £16 million is being pumped in to complete a new school for children with special education needs (SEN) after it emerged the project would cost five times more than expected.
Councillors agreed to provide the cash injection but warned the huge cost increase is equivalent to building four new primary schools.
Kent County Council's (KCC) education committee revealed the costs have gone up from the £4m budget approved in 2020 when the plan to revamp the former Walmer Science College in Deal was agreed.
The school will provide an additional 240 SEN plans as a satellite site of The Beacon on the Park Farm Industrial Estate in Folkestone – but is now set to cost £20m.
The former Walmer Science College in Salisbury Road closed 10 years ago.
The first phase of the new satellite school - which was originally estimated to cost £1.6m - opened in April 2021 and ended up costing £3.1m.
Planning permission for another two phases of the construction was granted last month.
When complete, the school will cater for pupils with autism and learning difficulties. It currently has 80 pupils.
A report presented to councillors ahead of a meeting of KCC's children's, young people, and education cabinet committee yesterday said costs for phase one of the project went up after the build commenced in April 2020.
This owed to a historic lack of maintenance of the buildings, and the need to replace electrics, heating, and data cabling.
A review of the buildings recommended that part of the college which had been built in the 1960s should be demolished and rebuilt as it couldn't be refitted to meet the needs of a special education school.
The review concluded another part of the site, which was built in 2004, could be retained.
The forthcoming works include building two blocks, the first of which will include 18 classrooms, therapy rooms, and a gym for Key Stage One and Two pupils. The second, for older pupils, will have 10 classrooms.
The total cost to complete the project is now just under £20m – 400% more than the original budget.
Councillors approved the release of just under £16 million to finish it.
Cllr Gary Cooke (Con), questioned why the costs had spiralled so much from what was originally agreed.
The Maidstone south and east representative said: "This is an additional £16 million that's not currently provided for in our capital programme, so what - as a result of agreeing this - are we not going to be able to do? Or what are we going to have to push further back on the capital programme?
"This is the equivalent of four primary schools; that's how much extra we're putting into this.
"The equivalent of four primary schools that we can no longer afford because of this one project, that's completely wrong."
KCC education officer David Adams said the original cost estimate for the project was "extremely poor" and said officers initially thought the college would be suitable to be brought back into use as it had been in use in recent years.
Cabinet member for education and skills, Cllr Rory Love (Con), said the cost per pupil place - £83,018 - was at the lower end of what would be expected for a special needs school and therefore the project was good value for money.
The Cheriton Sandgate and Hythe east councillor said: "It looks to be value for money, the issue is it's not quite as good value for money as we thought it would have been three years ago."