Principal Paul Marshall said unknown people came into the school grounds in High St overnight Saturday and made a mess.
"It looks like it might have been kids. They got into the skip bins and dragged out paints and other things and threw them around," he said.
"They've damaged a few tables and chairs and pulled out some cables from the computer data cabinets."
The school is in the process of relocating to its new campus at Twin Rivers Primary School.
"It's very annoying when we've put in a lot of work over the past few days to clean up the old school yard," Mr Marshall said.
"We've got a computer technician taking out the rest of the data cabinets now."
Mr Marshall said police had been contacted and urged anyone who knew anything about the damage to come forward.
"We would appreciate if the community could keep a close eye on the school and look out for any suspicious activity," he said.
Anyone with information is urged to contact Echuca police on 5483 1500 or Crime Stoppers on 1800 333 000.
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