The find came as a total surprise to staff and students as none of the current staff were at the school in 1981.
The school's foundation co-ordinator Victoria Hamilton decided to get in contact with the school's head boy of 1981 Sam Ritchie.
Ritchie, who now lives in Hamilton, said it was "quite out of the blue".
"I had driven past and saw the scaffolding on that end of the building and wondered what was happening."
Finding it has been "quite a surprise" for the school and past students and everyone is finding it "quite exciting", he said.
He said the time capsule was put in as the building was new. He thinks the contents include speeches from himself and others as well as newspapers.
Now the school plans to make their own time capsule.
Staff and students are still working out what to put in their time capsule but the school wants it to contain reference to the time period the capsule from the 80s was found which was the Covid-19 level 3 lockdown.
They want the time capsule to reference the impact coronavirus has had on the boys with online learning, experiencing lockdown and how important school life and friendships is to their daily routine.
The new capsule is likely to be put in the wall of the new performing arts centre in late term 3 or early term 4 before building is complete.
While it has strict instructions that it shouldn't be opened until 2031, Hereworth School Old Boys have shed a light on what is inside.
"Past staff and Old Boys from 1981 recall exercise books, school magazine, photos and even a calculator being included in the time capsule, calculators at that time were just being introduced into the school.
"Social media has enabled past staff and old boys to link up and share their memories of this time capsule being put together," the school said.
In the meantime, the capsule will be kept safe in a display cabinet in the Founders' Room – a special area in the school which displays its history and legacy.