From the start of the new academic year in September, Bishop's Castle Community College will be marking the anniversary of its opening in 1922.
In preparation the college hosted a 'centenary gathering' on Saturday, where people could take along their own historic photos and memories – and look at photos and displays already set up.
Students from the school were also conducting interviews with former pupils and staff as part of a living history project to be included in the celebrations.
Another idea is the creation of a time capsule – with an old school bell and a 1970s school recipe book already set aside for inclusion.
Reuben Thorley, headteacher at the community college, said they had been delighted with the number of people attending and wanting to share their memories.
He said: "We have had a large number of ex-students and staff coming through the building, looking at old photos, old class photos, old full school photos. They have been identifying people and putting post-it notes with names on there.
"It has also been about meeting old friends, people they might not have seen since primary school or secondary school, bumping into each other.
"We have got a student doing living history interviews of ex-staff and ex-students. They have got four former students who were all in the same intake in 1969 in there at the moment."
Mr Thorley said the aim was to "collect as much information as we can".
He added that he had been thrilled at the reaction to the event, and was looking forward to marking the major milestone.
"I am really pleased by the response from the public," said Mr Thorley.
"We were not sure how many people we were going to get. It was a slow start but it has built up and been constant this afternoon with a steady rotation of people coming and sharing photos and memories with staff in the school."