Yobs broke into the grounds of a Bolton school and caused thousands of pounds-worth of damage.
Improvements to Bolton St Catherine's Academy new primary centre have been delayed because of the vandalism.
The school, in Breightmet, Bolton, will have to cover the costs of damages construction machinery and outbuildings.
Police have urged parents to keep an eye on their kids following the incident on Monday evening (March 2), beleived to have involved two youths.
Head Rachael Lucas shared images of the damage to a JCB telescopic handler. Its windows were smashed.
Mrs Lucas said she believes the culprits are St Catherine's students, but that she didn't want their actions to reflect poorly on the rest of the children - or the school.
She said: "It's massively disappointing and the thing that's frustrating is that it's not representative of our student body.
"I feel incredibly strongly that the actions of two students should not tar the rest of the student body who would not dream of doing such a horrendous thing.
"In fact, the kids have been really horrified when we shared it with them."
Although the academy is owned by the Bishop Fraser Trust and run independently of Bolton council, Mrs Lucas said the town hall is funding improvement works due to the need for extra primary provision in the borough.
The work involves converting classrooms to accommodate more pupils, making it a two-form entry facility.
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Following the incident, GMP Bolton North posted on Facebook: "In the last week, we have had numerous reports of youths entering the grounds of Bolton St Catherine’s Academy and causing thousands of pounds worth of damage to machinery and outbuildings.
"There is currently building work on going to improve the facilities to students at the school and this damage is hindering this."
Mrs Lucas added: "It's delayed the build massively which is impacting on the provision of the primary students, which is unacceptable and massively disappointing.
"The police have been amazing though, they're really proactive.
"They've put more patrols around the building and they shared this on social media for us. I think it's a really good model of the school and police working together sharing information."
