A 17-year-old high school student has been charged with setting fire to Whangamata Area School.
The school's technology department was gutted by a blaze last week.
Police and firefighters at first struggled to determine what caused the fire, which caused several thousand dollars' damage.
An investigation by police and the Fire Service had since established that the fire was caused by "the reckless use of matches", detective sergeant Martyn Hughes said.
The teen, who was charged with arson, appeared in Thames District Court yesterday and was bailed.
He would reappear in the Waihi District Court next month.