More than 80 arson attacks are carried out on Sussex schools each year.
Firefighters revealed the figures as they visited Tideway School in Newhaven to point out it was only a matter of time before arsonists killed someone in the county.
They chose the school to hammer home the message of how dangerous fires can be.
Tideway was wrecked by a fire, which was started deliberately, causing £3 million of damage in April last year.
Adrian Brown, senior fire safety officer at East Sussex Fire and Rescue, said the fire brigade had to deal with 80 arson attacks at schools in Sussex each year. Nationally, about 25 fires a week are started in schools.
Mr Brown said: "It's a frightening amount. The fire service nationally is very concerned by the amount of arson in schools.
"The Tideway fire was one we knew was started deliberately and was one of the most serious we've seen in Sussex in a number of years.
"But we have a colossal amount here - about 80 a year. It is terrifying. The statistics are horrendous because there's only about 400 schools in Sussex.
"Our biggest concern is, historically, these fires were more likely outside school hours, now it is during them when the children are actually on the premises.
"There is a worry that if we don't nip this in the bud, there will be a tragedy."
A year after the fire at Tideway School, much of the damage to the library, staffrooms and 40 classrooms has yet to be repaired.
Mr Brown said revisiting the incident also raised the issue of what more could be done to protect schools from fire.
The fire service has promoted installation of smoke detectors for many years but sprinklers were the only answer, he added.
He said: "We've now got a dedicated arson reduction team offering free arson audits to schools.
"We advise them how to make their schools safe but the way forward has got to be sprinklers - that's the fire service's only answer."
Hove MP Celia Barlow has been granted an early day Commons motion on sprinklers in schools.
She said: "They prevent casualties, they avoid great property damage caused by the fire and water to extinguish it and they help to save water because they fight the fire in its early stages."
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