Once inside, he also used the piece of wood to smash tap faucets, causing the entire room to flood.
Shortcliffe then went to the opposite room and after smashing another glass door he threw musical instruments and furniture around the room, damaging some beyond repair.
An extremely drunk Shortcliffe was found by police as he was leaving the second classroom and they arrested him. He was too drunk to be interviewed that night back at the police station.
Judge Bidois told Shortcliffe his actions had resulted in a significant expense and clean-up time for the school and being drunk was no excuse.
"This was just mindless, wanton damage," the judge said .
Under further questioning by Judge Bidois, Shortcliffe revealed that he had indeed been a student at the college in 1998. "It doesn't make sense. If you can do this amount damage to your old school, what else can you do to other parts of the community? To do this was just mindless stuff," the judge said.
Judge Bidois noted Shortcliffe was on prison release conditions at the time after being freed from jail on March 21 after serving time for an earlier burglary.
Given Shortcliffe had received nine months prison late last year for burglary, there needed to be an escalation in the penalty, the judge said.
"But I can't impose reparation as you don't have the ability to pay."
Judge Bidois warned Shortcliffe that should he commit a burglary in the future, his time behind bars would be "years" rather than months and urged him to take advantage of his release conditions.
A Tauranga Boys' College spokesman, who spoke on condition he was not named, told the Bay of Plenty Times there was the major inconvenience of having two school rooms out of action for at least two hours while the clean-up took place which was disappointing.