The OBA was inaugurated on 25 March 1977

The OBA was inaugurated on 25 March 1977 when late S L A Ratnayake was the Headmaster. The College was then known as St.Thomas' Preparatory School.

The following were appointed as first Office bearers of the OBA.

The Patron
Rt. Rev. Cyril Abeynayake
Biship of Colombo

President
Mr. S.L.A. Ratnayake
by viture as Headmaster of the College

Vice Presidents
L.A. Adithiya, Ananda Alahakone

Hony. Secretary
Mr. Mithra Edirisinghe

Hony. Treasurer
Mr. Rodney Perera

10 Committee Members
P C Munasinghe, P Gunasena, G Jayawardena,
V P J Warapitiya, I M Razeek, G A D Anandapala,
Nayana Ellepola, Kavan Perera, B Galaboda
G Radhakrisnan.

Hony. Auditor
Mr. S V Ratnam

Mr.Mithra Edirisinghe, the Hon. Secretary OBA who was in the College staff together with Mr. Sandana Krishnan revived the OBA in 1987 with Mr. Welikala as the President then Headmaster of the College

Annual General Meetings were conducted in the years 1988,89 & 90. Once again the OBA went through a turbulent time with the prevailing situation in the Country. Mr. Chrishan Perera, Mr. Raja Sithambaram and Mr. Mohan Ellawela stood behind the Secretary, Mr. Sandanan Krishnan as it came to a brinx of collapsing, not only the OBA even the Schools Administration.
Mr. R. Herathge took office as the Headmaster of the College in 1989 and in 1990 he instigated the real transformation of the OBA which is now in existence. Mr. Herathge as the President convened a meeting of old boys who are living in and around Colombo to form the Colombo Branch on 14th June 1991.

On 14th June 1991 at the invitation of the Headmaster Mr.R.Herathge 40 old boys met at St.Thomas Prep. School, Kollupitiya to inaugurate the Colombo Branch of the OBA.

The following were unanimously appointed.

President
Ex-Officio the Headmaster - Mr R Herathge

Administrative Secretary
Mr Mithra Edirisinghe

Social Secretary
Mr Hiran Fernando

Treasurer
Mr Vasantha Wijesekera

Committee Members
Messers Manilal de Mel, Christo Gonawela, Ananda Alahakone, Sbash Kulasena, Mahinda Perera,Roshan Tissera

Donations amounting to Rs 31,240.00, made by a selection of members, were collected, in order to meet the Administrative Expenses of the Colombo Branch.

A total of 154 Old Boys, were enrolled as Members as at end July 1991. The Membership Fee for the Colombo Branch was Rs 100.00 while it was Rs 200.00 for the Main Branch.

The Colombo Branch proposed that Constitution of the Main Branch be Amended to be in accordance with the Constitutions of the OBAs of S. Thomas’ Colleges, Mount Lavinia and Guruthalawa. This was adopted at the AGM.
The first ever raffle organised by the Colombo Branch brought in a net profit of Rs 106,570.00. It was decided to donate all Class Prizes at the Annual Prize Giving of the College in 1991.

The Colombo Branch of the OBA was amalgamated with the Main Branch on 25 July 1992, at the 2nd AGM of the Colombo Branch. The Life Membership Fee of the OBA was increased to Rs 300.00.

The Golden Jubilee Celebration of the College took place in 1992. The OBA organized a development fund. Rs 145,000.00 were collected through the Development Fund Card. A car sticker was printed to mark this occasion.

For the second successive year, the OBA contributed Rs 15,000.00 towards College to cover all Class Prizes given at the Annual Prize Giving.

The renovation of the Peiris Dorm was the first major project to be handled by the OBA. The Executive Committee, shouldered the complete responsibility of the entire OBA Membership and undertook the task of renovating the Peiris Dorm at a cost of Rs 528,055.15.

The renovated Peiris Dorm was ceremonially handed over to College on 9 March 1994.

The inaugural S L A Ratnayake Memorial (under 16) All Island Badminton Championship was held in College in April 1994. This was sponsored by the OBA. Mrs S L A Ratnayake graced the occasion as the Guest of Honour.
The first Career Guidance Council Seminar was held in College for School Levers on 30 October 1994. The following were the Members of the Council.

Chairman
Mr. Upali Panditharatne

Secretary
Mr. Niranjan Fernando

Members
Mr. Christo Gonawela
Mr. Anada Alahkoon
Mr. Hiran Fernando
Mr. Dehand Senanayake

The objective of the Career Guidance Council is to help prepare students and school leavers in the process of choosing and deciding on a career, handling the application process and facing the all-important interview.

“Ball ‘42”, the inaugural dance of the OBA was organized at the Holiday Inn on 10 September 1994. The Organising Committee headed by Mr Christo Gonawela did a tremendous job to organise this colourful event very successfully.

The respective Executive Committees of the OBAs of Guruthalawa, Bandarawela and Kollupitiya appointed Mr Clifford Ratwatte as the Board of Governors Representative of all three schools.

The second S L A Ratnayake Memorial under 16 All Island Badminton Championship was organised in Colombo and Bandarawela in April.

For the first time, an AGM of the OBA was conducted in Colombo, due to the non -availability of the College premises. A record of 107 members attended the Ninth AGM and the Fellowship Dinner.
The Career Guidance Council conducted the Workshop for the final year students of the College, for the second time on 9 November 1996.

On 14 December 1996, a day get-together was organised at the CR&FC Grounds at Longdon Place, Colombo 7. 86 members and their families participated.

The 1996 Raffle recorded net profit of Rs 14,130.00

On 27 September 1997, a Members Night Get-together was organized at the Hotel Inter-Continental. Its was the most successful get-together organized to date. It gave a net profit of Rs 116,556.84 where around 105 Members attended.

Career Guidance Council carried out their seminar for school leavers on the 29 November 1997 in College

Cum Get-together was organized on 17 January 1998, at Dunhinda Falls Inn, Badulla. Executive Committee Member, Mr Saman Wijesekara with the help of Messrs Suresh Subram, Mahinda Alwis, S Kamalanathan, A C M Tharick, Hemantha Alwis, Trehan Rowlands, Hasantha Wickramasinghe, S M Iqbal and M Najeem, headed the Organising Committee.

The Organizing Committee of Badulla helped 101 new Members to be enrolled during the Badulla Membership Drive.