A Freedom of Information request by the organisation revealed the contract cost of PPP will total nearly £12.9m between 2016/17.
The bill includes the cost and maintenance of Arran High School, Greenwood Academy, St Matthew's Academy and Stanley Primary.
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The findings come during widespread calls for a safety review of all PPP contract buildings in Scotland.
Seventeen schools in Edinburgh were closed last week after serious construction defects were uncovered in the buildings.
GMB Regional Organiser, Paul Arkison, said: "These payments are an obscene waste of local taxpayers' money and particularly at a time when NAC has imposed £13.6 million worth of cuts to local services.
"It is morally wrong that local hard-working families are lining the pockets of big business to ensure their kids' education while local community services are being decimated.
"Councils should be looking at every option available to them in order to renegotiate these contracts, which look increasingly like a heist on the public purse."
Mr Arkinson added GMB Scotland supports calls for a review of all PPP contracts across Scotland.
(LM)
