It was reported in September that thieves had also attempted to steal copper from the toilet block.
The spokesman said the demolition work was due to be completed by the middle of January.
The property was no longer owned by the education ministry, but had been transferred to the Office of Treaty Settlements in November.
The school's disposal process would now be largely determined by the requirements of the Public Works Act 1981. This involves five stages, which could include placing the property on the open market if it was not land banked for future settlements.
Lands Trust Masterton previously said it planned to sell its portion of the school land to the government Office of Treaty Settlements.