According to Mr Missen the school is as old as the community itself, appearing quickly after the land was drained, allowing dairy farms to spring up from swamp.
"The school became the hub.
"There wasn't a church established until the 1950s. The church first met in the school."
The second building was added in the 1950s, with prefab classrooms added in the 1980s.
When the original building was extended, the whole building was renovated to reveal a beautiful Victorian-style vaulted ceiling.
Mr Missen said when the fake roof was removed it revealed a small window which it transpired had been left open for decades.
"The air would blow in and the manhole would move up and down.
"The kids had this theory that it was the ghost of Horsham Downs," he said.
The school experienced a boom in 2008 when $2 million was granted for the creation of eight new classrooms to accommodate a growing population.
Mr Missen said the school quickly had a surge of new students coming from town.
Despite up to 75 per cent of the students coming from within the city boundary the school still holds calf days and maintains an enviro area, complete with free range chickens.
"We have local farmers who lend calves to the town kids so they get the opportunity to rear the calf," Mr Missen said
In 2015 the school also won the Treemendous makeover competition from the Mazda Foundation, and a whole area was planted with native trees.
Over the years the school has had a tennis pavilion come and go, and two pools. The first pool was completed in the early 1950s, and was demolished to make way for a second in 1972.
The first had to be demolished when the concrete structure began to crack, and Mr Missen said the rural community decided the easiest method to remove it would be to use explosives.
"There was a raffle to raise money for the new pool and the prize was for a pig - but the pig rotted and the proceeds for the raffle were reduced somewhat because of that," he said.
The centennial celebration programme includes a school assembly at 9am on Friday, February 26 followed by an open day and a mix and mingle from 6-9pm.
National MP Tim Macindoe will open the school's new multipurpose room which was completed in late 2015.
On the Saturday from 10am there will be a welcome with speeches, entertainment and burial of a time capsule.
"We are going to put in old uniforms, photographs, the jubilee booklet, newspaper clippings, lots of stuff ... it's a properly sealed chamber that should last the next 25-50 years."
A new sculpture will be unveiled at the front of the school. It consists of three totem poles topped with symbols representing the school's three principals as thinking learners, good citizens and self managers.
A centennial dinner will be held at The Atrium at the Wintec campus on the Saturday night.
Notable names to pass through the school include Rushlee Buchanan, who is part of the New Zealand cycling team, and international motorcross rider Josiah Natzke.
Those interested in attending any of the celebrations can visit www.horshamdowns.school.nz/centenary
