Twenty of Sydney's wealthiest private schools received $111 million in taxpayer funding last year, new data has revealed, allowing the institutions to subsidise plans for tennis courts, flyover theatre towers, and Olympic pools with underwater cameras.

The schools, including The King's School, Trinity Grammar and SCECGS Redlands, have offset parents investments through the public purse courtesy of an $11 million increase in combined state and federal funding since 2012, according to MySchool data.

On Friday, Fairfax Media revealed that the oldest girls school in Australia, St Catherine's in Waverley, had won a battle to build a $63 million auditorium complete with an orchestra pit, a water polo pool, and a flyover tower for state-of-the-art theatre productions.

It is one of several multi-million dollar developments underway at schools across Sydney, where five of the most expensive institutions have received more than $92 million in state and federal government funding since 2012, equivalent to the total cost of building up to three new public schools.