It was established in 1789, making it one of the oldest schools in India and has the largest campus in Kolkata is a Kindergarten to Higher secondary school for boys located in 4, Diamond Harbour Road, Kidderpore, Kolkata, West Bengal-700023 Kidderpore, India. It has one of the largest campus areas in the city of Kolkata comprising of three football size fields, one basketball court, and children’s playgrounds. The campus also houses the St. Thomas’ College of Engineering and Technology and has a church called the St. Stephen’s Church. The school has adjacent division .The students of this school are nicknamed as Thomasites (boys). The school is affiliated to the Council for the Indian School Certificate Examinations (ISC), which conducts the ICSE (Grade 10) and ISC (Grade 12) examinations over the country. In 1790 a 15 bigha plot with a house was bought at what subsequently came to be known as “Free School Street”. Both the boys’ schools operated from there. Today part of the land houses the food and rationing offices. It was only at the beginning of this century that the authorities decided that the “Free School Street Premises” was “Unsuitable” and thought of shifting the school to Ranchi.
The idea was abandoned as parents objected and the choice fell on “Kidderpore House” at 4, Diamond Harbour Road. In 1914 the “Free School Society” approached the government for “Kidderpore House” and the school started in full from there in 1916. In 1917 it was decided, that the “Free School” would be converted, into the St. Thomas’ School for better management and in 1923 the “Calcutta Free School” was officially named St. Thomas’ School after the Apostle on whose day the original “Free School Society” had been founded. World War II saw “Kidderpore House” converted into a military hospital and the school was shut down. The boys’ section was shifted to Takdah near Darjeeling. With the war coming to an end the boys were shifted onto the campus for the first time. There were radical changes after independence when the Viceroy and Governor General left India and the nation’s President became patron and the school opened door to non-Europeans and other communities. Over centuries the sky like at “4, Diamond Harbour Road” has been interspersed with new buildings that have come up to accommodate the boys.