A vandalism rampage by a gang of louts at the historic Strabane Grammar School has caused £30,000 of damage.
Petrol and paint bombs were hurled at the building during the attack on July 12, which left the sixth-form study, housed in the gate house, gutted.
Classrooms were also paint-bombed, walls were damaged by hammers, 70 windows were smashed, trophy cabinets were shattered and a computer monitor was destroyed.
The spiralling repair bill, which could yet include the cost of replacing a roof, has been put at tens of thousands by vice-principal Richard White.
Mr White does not believe the attack was sectarian, despite the school being hit on the Twelfth night.
It was also the target of violence on July 11 last year.
He said: "When I arrived at the school and saw the extent of the damage, it was hard to take in.
"The ground floor of the gate house is destroyed from the amount of water the fire service needed to extinguish the blaze on the second floor. I don't think it can be used again.
"They were able to put the fire out without removing the roof tiles, but we don't know yet if they will need to be replaced.
"We think we are looking at a repair bill of £30,000, but it could be more than that.
"As well as the paint and petrol bombs, they smashed every window they passed - a total of 70 were broken."
And Mr White branded the vandalism as "wrecking for the sake of wrecking".
He said: "They took a hammer to the walls and smashed the trophy cabinet and crystal trophies the students had won over the years - that stuff is irreplaceable."
Although this is not the first attack the school has suffered since the summer break, it is the worst, and word about it quickly spread to the 400 pupils.
Mr White said: "Thankfully the students are not at school, but between Facebook and other social network sites, word quickly got around and they are shocked and very upset. Some came to help clear up.
"This school is part of the community and our students are from both sections - so this was an attack not on a building, but on the community."
And Mr White said the destruction had cast a dark cloud over plans for a schools' merger in the new school year. "We were looking forward to a new era in September when we merge with Strabane High School to become Strabane Academy. Our focus was not this devastation.
"The money for repairs will be taken from a budget somewhere where it could have been better spent."
CCTV footage of the gang of six thugs is forming part of the police investigation.
The PSNI and local politicians have appealed for information.
Cllr Patsy Kelly said he was "disgusted" at the vandalism. "The attack on this school is utterly shameful," he said. "Pupils will suffer as teachers will now be tasked with finding funds to repair the damage out of their already over-stretched school budget. There can be no justification for this destruction."
Strabane Grammar School was once the family home of Cecil Frances Alexander, (right) who wrote famous hymns There is a Green Hill Far Away and All Things Bright and Beautiful. Her book, Hymns for Little Children, became a classic, helping to fund a school for deaf children in Strabane.