The demolition of the old Cornwall St School buildings began this week after the school was targeted by vandals.
Contractors Bruce Buchanan began demolishing the disused school's old bike shed and bus shelter on Monday.
The school was built in the 1950s and closed in 2004 as part of a Ministry of Education review that saw seven local schools closed.
The Masterton site has not been used since and has become a target for vandals.
"The buildings have been targeted by vandals and it was decided to remove them in the interests of keeping the site safe," said a Ministry of Education spokesman.
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.