Tyres were placed under two Hamilton school buildings and set alight in the second arson attack on the school in six years.
Hamilton police are now urging anyone with information about the blaze - early yesterday morning - to contact them.
Firefighters were called to Hamilton East Primary School about 6.50am.
Detective Senior Sergeant Ross Patterson of the Hamilton CIB said after firefighters extinguished the blaze they discovered how the fire began.
"Two buildings at the school, the hall and a dental clinic have suffered varying degrees of damage after tyres were placed under a wheelchair access ramp and under the clinic and set alight."