Mary, an alumna of Miss Porter's School, was the great-granddaughter of Caleb Atwater (1741–1832), a Connecticut merchant magnate who supplied the American forces during the Revolutionary War.

In 1775 General George Washington visited the Atwater store in Wallingford en route to assuming command of the Continental Army.

[6] In 1889 Mary planned a new institution on the same principle of female self-sufficiency and she advertised in The New York Times for a headmistress to run a school that would train girls in the "domestic arts."

Ruutz-Rees (pronounced "Roots-Reese") quickly changed Rosemary Hall's mission from "domestic arts" to that of a contemporary boys school.

Her personal curriculum for the next four decades had three core components: student self-government, contact sports, and a brutal workload of academics.

The official history of Choate Rosemary Hall, written by Tom Generous, says that the rift between Caroline Ruutz-Rees and Mary Choate, proponents of two very different sorts of feminism, was public knowledge as early as 1896, in which year headmistress and founder did not share the lectern at Prize Day and local newspapers published "denials" of a rumor that Ruutz-Rees would leave the school.

[10] But by 1900 the headmistress and her educational style had acquired influential champions among the students' parents and two of them, residents of Greenwich, Connecticut, a wealthy enclave twenty-five miles from midtown Manhattan, joined forces to effect the removal of the school to their town.

Julian Curtiss gathered a group of investors and established a joint stock corporation funded through the sale of six-percent bonds.

The Greenwich residence of Rosemary Hall began in fall term 1900, when 57 girl students moved into the Main Building, known as "The School," a U-shaped shingled house on Zaccheus Mead Lane.

In the next two decades the campus would build or acquire other "cottages" and lay out an Italian garden, the gift in 1912 of Janet Ruutz-Rees, mother of the headmistress.

The heart of the campus was St. Bede's Chapel, built with $15,000 collected at bake sales, teas, and benefits, and from every constituency of the school.

According to the November 25, 1909 issue of Leslie's Weekly," it was "begun three years ago by the girls themselves who collected stones and carried them one by one to the spot which the building was to occupy."

On October 17, 2009, the centennial of St. Bede's was celebrated in Greenwich by Rosemarians past and present, with the Whimawehs singing traditional RH songs.