Moreton Hall School Trust, in Bury St Edmunds, has bought the freehold to the school buildings and 30 acres of parkland it occupies.
The multi-million pound deal, which was announced on Tuesday, might not have been possible if it had not been for the current economic climate.
Michael Whatley, chairman of the governors, said: "Paradoxically, the timing of the sale has been good for the school as property prices are reasonable and interest rates are low."
The school trust has been hoping to buy the freehold to the school, which was founded in 1962 by Lady Miriam Hubbard and her husband Lieutenant Commander Peregrine Hubbard, for a number of years.
Benedict Dunhill, headteacher, said that while the governors had worked hard to put the financial backing in place, the support of the founders' descendants had been crucial to the deal taking place.
"It is a testament to their spirit of magnanimity that we have been able to secure the long term future of the school," he said.
The school will outline its plans for short, medium and long term development shortly.
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