The School is divided into five Houses, each named after an individual who has contributed to the foundation and development of Trafalgar. They are Barclay, Cumming, Donald, Fairley and Ross.  Each House is identified by its own colour and is made up of girls from each grade.

Individually, students contribute to their Houses by winning points in work, games, and conduct. Extra-curricular activities such as sports, drama, outside reading and contributions to the School magazine also help in the accumulation of points.

Collectively, the Houses compete with each other in various sports and activities. The most important inter-House event is the annual Drama Competition. At the end of the year, a trophy is awarded to the House which has earned the highest number of points. In this way, public spirit and co-operation are encouraged, as each student works not only for herself, but for the group as well.

Since the members of each House are from all grades in the School, a girl has the opportunity to establish friendships outside her own class and thus widen her interests. It also gives the senior students a chance to develop leadership qualities while working with the younger girls.