The painting by French impressionist Henri Le Sidaner was donated to the district in 1933, but school officials somehow lost track of it until January.
On Wednesday, the 40- by 32-inch painting titled "Interior" brought $750,000 at an auction in New York's famed Sotheby's, which waived its selling costs. The painting was expected to bring $350,000 to $450,000.
The district opted to sell the painting because most of the artists in its collection are from the Pittsburgh area, and because the painting is too valuable to display in a school.
Superintendent Linda Lane and others watched the auction online and said, "We're all pleased it went as high as it did."