Senior Sergeant Steve Aitken, of Dunedin, said a neighbour reported a fire at College St School in Caversham early on Saturday.
When firefighters arrived, the small fire was nearly out, but it was apparent someone had dragged three wheelie bins to the classroom door and set rubbish alight, Snr Sgt Aitken saidThe fire damaged the entrance and wall of one classroom.
Last week, Dunedin police raised concerns about a spate of rubbish fires in the city.
An empty College St property was damaged late last month, after rubbish bags were piled up and set alight.
In the past 10 days, bags of rubbish have been set on fire outside a church on the corner of Melbourne and King Edward Sts, another in a rubbish bin at Queen's High School in Surrey St, and a rubbish bag was set alight at the rear of George St stores.
Police believed at least the Melbourne St and Queen's High School fires were possibly linked.
Anyone who witnessed anything suspicious at the time of the fires was asked to contact Dunedin police.
