Four youths have been charged in connection with a series of incidents at the old Ellon Academy.
Police in the town are urging parents to make sure they know where their children are, after the school was targeted by vandals.
Officers were called to the school, at Schoolhill, on Friday and Sunday after being alerted by the public about suspicious behaviour.
Four children aged between 13 and 15 have subsequently been charged for various offences, and will be reported to the youth justice management unit.
Sergeant Andy Sawers said: “The school grounds are currently in a poor state and certainly not an area where any person should be.
“I cannot emphasise how dangerous the area is, and anyone who enters the site is putting themselves at serious risk. It is boarded up for a reason and I would plead with anyone, of any age, to not go near it.
“I would also like to remind anyone who attempts to enter the site or gain entry to the buildings that they could be arrested and reported for criminal offences.
“Likewise, anyone caught vandalising the property will also be dealt with. I would ask all parents in the area to ensure that their children are made fully aware of the dangers of such behaviour and the potential for criminal proceedings.”
He also encouraged the public to continue reporting any suspicious behaviour they see at the site.
He was echoed by Ellon councillor Isobel Davidson, who said it was “disappointing” four youngsters had been arrested.
She added: “It is important that parents know where their children are and what they are doing – the parents are responsible for children of that young age and make sure they are not misbehaving.
“It is a very dangerous site and entering the site you are putting yourself at risk, no one should be there.”