Arran High School cost North Ayrshire Council more £2.3 million last year in payback charges.
Arran is one of four schools in the area built under controversial PPP agreements, the others being Greenwood Academy, St Matthews Academy and Stanley Primary.
Together they cost the council £12,492,144 with the Arran share £2,330,440.
The figures came from a Freedom of Information Request (FOI) submitted by GMB Scotland. Under PPP agreements set up by the council, firms front up the cash for investment projects such as schools, but are then paid back amounts from the public purse over decades-long contracts.
They are popular because the initial outlay stays off the council’s balance sheet – but the taxpayer often pays up to 10 times the cost of the project.