Mansion House School opened in 1808 and became the Oxford County School for Boys in 1840. From 1908 to 1948, it was used by the Thame Girls’ Grammar School.

In 1917, when Miss May Hockley and Miss Clara Messenger took over, there were one hundred boarders and a similar number of day pupils.

A long line of buildings stretched behind the Mansion House, nearly to Southern Road. These included a large dining hall and assembly hall, a gymnasium (with sprung floor), and a swimming pool. In Moreton Lane there was a playing field with tennis courts, hockey and netball pitches.