The globes, dated 1825, were unearthed by a parent during a clear-out at Portishead primary, Bristol. With a diameter of 21 inches, they are the largest pair made by the Cary Company, one of the leading English globe-makers at the time.
David Rees, associate director of the Bristol Auction Rooms, said: "The standard library globe was 18 inches, so a 21-inch globe is the bee's knees. We thought they may have come from a large country house near Portishead, called Kingsweston House, whose contents were disposed of in the 1930s."
Mike Scriven, Portishead's headteacher, was not able to make it to the sale but a parent rang him from the auction rooms. "When I heard the globes had been sold for pound;10,000 I was stunned, delighted and amazed," he said.
The school is due to move into a new pound;2.2 million building in October and the cash raised will help fund outdoor activity equipment.
Its treasure was discovered in cellars beneath classrooms in the main building by parent Toby Stride. The cellar under the first classroom contained only old tables, chairs and benches.
"Then he went through a narrow entrance and in the corner he found one globe," said Mr Scriven. "He recognised that it could be something special.
The globe was fairly damaged but intact. He also saw the date 1825 on it.
At the far end of the cellars he found thebadly-damaged second globe.
"It is wonderful to find these real treasures below our feet."
Another unrealised treasure owned by a school was the painting The Daughters of Eve by George Dunlop Leslie, which hung in the hallway of Llantarnam comprehensive, Cwmbran, for 40 years.
It was bought for less than pound;300 and sold at auction for pound;170,000.
The discovery at Portishead will be shown on the BBC's Cash In The Attic series later this year