Robert Pelton Sibley (March 26, 1879 - November 3, 1957) was an American academic and a headmaster of Deerfield Academy. Born in Westfield, Massachusetts, Sibley graduated from Amherst College in 1900. At commencement, he was awarded the prize in oratory, a victory reported in the New York Times. From 1900 to 1902, he was the fiftieth head of school, or principal as the position was then known, of Deerfield Academy. He was succeeded by Frank Boyden. In 1903, he graduated from Columbia University with a Master of Arts degree. In 1934, he became the second husband of , the widow of James Wickham.