Arsonists appear to have struck at Redwood School leaving one classroom partially damaged.
Emergency services were called to the Prestons Rd school on Friday at 11.50pm after reports of a large amount of smoke.
Firefighters found a small fire in a classroom.
Specialist fire investigator Bruce Irvine said he believed the fire started outside the classroom when a picnic table was set on fire.
He said it was now school holidays, which meant schools were at risk and this would not be the last suspicious school fire.
“It is the start of the silly season, and they (schools) are at risk,” he said.
Due to the risk of asbestos contamination from material in the classroom, investigators wore full suits while they worked.
“All the asbestos product has been taken away,” Mr Irvine said.
He said schools should take a little bit of time and look at where things are being stored to prevent opportunists from having easy targets.
Police are investigating.