When girls join HMSG, they are assigned to one of four houses: Bagnall Oakeley, Imbert Terry, Mather Jackson, or Prosser. House allocation is usually random, however, any past family connections will be maintained, so sisters, mothers, and daughters will all be in the same House.
Girls stay with the House throughout their time at the School and this gives a marvellous chance for girls to mix across all the age ranges and to have a sense of belonging and continuity during their school years. Weekly house assemblies and house activities foster and support the pastoral aspect of the Houses.
Girls represent their houses at the annual Eisteddfod and Sports Days and they compete in House sport competitions in netball, lacrosse, rounders, swimming, hockey, cross country, rowing, badminton and tennis. Other events have included a bake-off competition, challenge quizzes, scarecrow and paper dress making competitions.
In 2011 buddy groups were introduced into the house system; about 12 girls from a full range of year groups team together for various fun quizzes and competitions during house assemblies. The girls have chosen their group names and designed logos for them. The quizzes and competitions focus on developing confidence, teamwork and learning social skills. The house structure also helps to ensure that day girls and boarders are fully integrated.
The first 'Divisions' were introduced to the School in 1913. These were known as Bach, Beethoven, Chopin, and Wagner, and were compiled automatically from the registers so that each Division contained both day-girls and boarders. Later, these Divisions, now called Houses were re-named after Governors who had given devoted service to the School, Bagnall-Oakeley, Imbert Terry, Mather Jackson, Prosser - and each House under its own House Mistresses began to develop its individuality.