Although the twentieth century had witnessed the greatest amount of change in the school the first quarter saw the school operating with fairly narrow limits with regards to size and activities.

In 1901 a new scheme was drawn up by the School's commission and approved by the Governor. It stipulated that "Foundationers" should be between the ages of 9 and 14, and that paying students would continue to pay £8 annually or £6 in case of students from the same family. No scholar should be admitted under 9 years or kept over 16 years, unless showing marked ability and recommended to the Trustees by the Headmaster.

In 1903, a junior department was started in the Headmaster's residence which was then a two storey, wooden building adjoining the school compound. The ‘Castle’ as it was called, was supervised and taught by a second Mistress with the assistance of the Headmaster.

There were 70 pupils on roll in 1907 and, for the next 32 years the number varied upwards and downwards from this figure reaching a peak of 95 between 1914 and 1919, and 57 in 1939. The decline in numbers was due to the opening of schools such as St. Hildas, Munro and Jamaica College in other parts of the island which offered superior boarding facilities and instruction in Science subjects.

The period around 1915 saw the erection of the "Old Building", the present library and the Headmistress's house (now the Personal Development Centre) as well as the 'buggy house' (the old library) These buildings have remained as outstanding landmarks on the Manning’s compound.