Boys are admitted to St John's at various stages.

In the Preparatory School the main point of entry is at Entrance Grade (formerly Grade 0). A few vacancies do become available at other levels from time to time.

In the College, the main point of entry is at Remove (Standard 6, now Grade 8). Prospective pupils are required to write an entrance test and a confidential report from the pupil's primary school Principal is requested. Each pupil's application is carefully considered and, in addition to his performance in the entrance test, his interests and cultural activities, sport and the report on his general discipline are taken into consideration before acceptance. Special consideration is given to siblings, sons of Old Johannians, sons of Clergy and those who come from a disadvantaged background.