In 1916, a group of 15 families in
Marin County, California, pooled resources to start a local
private school. The Little Gray School was finished in 1917. It began as a coeducational primary school, for students in grades 1–4. In 1918 it added intermediate and upper levels, both of which were limited to girls, and was renamed the San Rafael School for Girls. In April 1920, the school's trustees appointed two co-headmistresses, Katharine Fleming Branson and her sister Laura Elizabeth Branson. The elder of the two sisters, Katharine Fleming Branson, was Associate Director of Studies at the
Beard School in
Orange, New Jersey. Laura Elizabeth Branson was a teacher of mathematics and science at
The Shipley School in
Bryn Mawr, Pennsylvania, and had formerly served as head of the Department of Mathematics at
Rosemary Hall in
Greenwich, Connecticut. Both sisters were cum laude graduates of
Bryn Mawr College. A former student has alleged that the school condoned teacher and student relationships. There was also a law firm report that illustrated the permissive culture of the school. The school initially seemed to take the investigation seriously. The actual report that named four sex offenders sparked an investigation at University High School where the coach Randy Taylor was employed after Branson.
Coeducation The division of the two schools by gender started to become obsolete by the 1980s, as the two schools shared faculty, trustees, and curriculum. In July 1985, The Katharine Branson School and the Mount Tamalpais School were merged as a coeducational private day school, The Branson School. ==Campus facilities==