Celebrations to mark 60 years of education at Holy Child Primary School almost went up in smoke after an arson attack on the building on Monday night.
The efforts of firefighters, who tackled the blaze from 9.30pm to midnight meant the damage was contained, but school principal Orla McDonald said it was a horrendous experience.
The school in the Creggan area of Londonderry opened as normal after the fire, which was started on the roof of the building.
Police and the Northern Ireland Fire Service are continuing to investigate, but it has been established that the fire was deliberate.
Ms McDonald said: "There is some work being done to the roof of the school and the building material was set on fire.
"At a governors' meeting earlier we were discussing how we were going to celebrate the 60th anniversary of the school, but we very nearly didn't have a school by the end of the night.
"This school is at the heart of the community but there is an ongoing problem with children coming on to the school grounds.
"I would urge every parent to sit their children down and talk to them about the dangers of coming on to the school when they shouldn't. It is a very, very small minority of children who engage in this kind of behaviour but it is important that all parents sit their children down and have that chat with them."
The PSNI in Derry is appealing for anyone with information to contact officers in Strand Road on telephone number 101.
If someone would prefer to give information without giving their details they can contact the independent charity Crimestoppers anonymously on 0800 555 111.