Two girls and one boy have been arrested following a number of incidents at a school in Bognor, according to Arun Police.
In a post on social media, the district police force said its prevention and response teams are 'providing additional patrols' of The Regis School during the day and night 'in light of recent criminal damage and anti-social behaviour'.
It added: "A 12-year-old girl has been arrested on suspicion of criminal damage, burglary and assault and a 13-year-old girl on suspicion of burglary.
"A 13-year-old boy has also been arrested on suspicion of going equipped, criminal damage and burglary - all have been released under investigation whilst we continue with our enquiries."
The Regis School confirmed it has been 'targeted by a particularly unpleasant and costly form of vandalism', along with 'other locations in Bognor Regis'.
A spokesman added: "It is very disappointing and distressing to our community that this damage has been done.
"Everyone at The Regis School is concerned that those responsible are caught and prosecuted and we will be supporting the police in any way we can to ensure that the perpetrators are brought to justice.”