Several Auckland schools have had their windows smashed and vehicles damaged in recent days.
On Facebook, Massey High School said they, and at least four other West Auckland secondary schools, had suffered similar "mindless vandalism" over the past two nights.
"All schools have suffered similar damage, large numbers of broken windows at the front of the school (caused by blunt objects) and damage to school vehicles," the post said.
Green Bay High School principal Fiona Barker said there was a "significant amount" of damage, and staff and students were disheartened.
CCTV footage showed five people entered the property about 4.30am and smashing 30 windows across multiple classroom blocks, as well as the windows out of three school vans.
"The damage is significant both cost-wise, but actually the disruption is huge," she said.
Intermediate school students were due for a "transition visit" at the school on Friday and that had to be postponed.
Students had to be moved into different classrooms to avoid the damage, and a big clean-up had begun.
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"It's also such a hard way to end the term, really disheartening for our kids to come into school, and our teachers, and to find all of this happening."
Barker did not have any idea why anyone would have vandalised the schools.
"It just looks mindless, nothing was stolen, it was just causing damage ... just so much damage."
Barker estimated the clean-up cost would be "in the many tens of thousands" - money better spent on "doing great things for kids to enjoy", she said.
Massey High School principal Alastair Fairley said a large number of windows at the front of his school were smashed using blunt objects, and school vehicles also had windows smashed.
"Obviously incredibly frustrating, the disruption it causes is unwelcome and the mindless nature of it can seem a bit unbelievable," he said.
"Our student's response is heartening as they are immensely proud of their school. At least no one was hurt."
Fairley said the schools were working together with police, and the Ministry of Education has been quickly facilitating claims.
"The collegiality amongst West Auckland principals really comes to the fore with incidents like this," he said.
Several Auckland schools have windows smashed
Lynfield College principal Cath Knell told Midday Report three classrooms, four offices and the marae had been damaged at her school.
She said two "masked offenders" entered the school grounds just before 4am.
"What they've used has shattered the windows, in some cases they've broken and left jagged glass through the classrooms, so those classrooms are all out of action," she said.
She said the school was holding its year 11 prizegiving today, and they have had to move students to different classrooms to avoid the damage.
Meanwhile a primary school in the area told parents it was installing extra security cameras after the string of crimes.
"Recent incidents of vandalism in our local area, including at Rutherford College, have highlighted the importance of being vigilant about safeguarding our kura," said a letter from Matipo School.
It had not been vandalised but "faced some minor security challenges" after hours, the letter read.
"To address this, and to ensure our beautiful school remains a place of pride for all, we will be installing external security cameras around the school in the coming weeks."
Vandalism takes money away from education - Secondary Principals Association president
Secondary Principals Association president Vaughan Couillault said it was hard to pinpoint who might have carried out the vandalism.
"Normally school students don't come back and vandalise their own place because generally they respect it. My experience would say it's likely to be borne of some conflict or some unresolved tension, or just drunken behaviour."
Couillault, who was also the principal of Papatoetoe High School, said most schools had experienced some sort of vandalism in the past but it was usually isolated behaviour.
He said the cost could run into the thousands if multiple windows were smashed or extensive damage was done.
"A couple of years ago we had some damage to a fence that was repaired and then it was knocked down again. That went well into the tens of thousands of dollars to repair.
"And it literally just takes money out of the classroom. So if you're having to spend money on additional vandalism stuff, yes there are ways you can get to the ministry and get some additional support for that, but it literally takes money away from other good educational purposes."
Couillault said school principals would be double-checking CCTV systems and affected schools may introduce random security patrols.
"The thing is, people will know who it is and it just takes one sensible person to let us know and we follow that lead and the problem goes away."
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