Pupils returning to Ballyclare High School in September 1986 were welcomed into new state-of-the-art facilities.
The second phase of the £3.3 million extension project was completed three months ahead of schedule, and meant that the new building was ready to use after the summer break.
The three storey central block housed maths, geography and history classrooms, as well as staff facilities and common rooms.
The final phase of the work was due to be completed by March 1987.
This final section would include a two storey biology and library building, as well as a single storey sports block.
The work was being carried out by the construction firm Blackbourne and McCombe.
Cedric Blackbourne, who was directing the project, said that one of the most important aspects of the contract had been to avoid disruption to school work. Mr Blackbourne said that they had been able to do this with the help and support of the teaching staff and headmaster, Mr Cecil Millar.
The school has undergone further development work in recent years, including the construction of a new library and drama studio.