Police in Chorley have issued a warning to youths who have been climbing on school roofs and vandalising property saying that their behaviour will "not be tolerated".
Officers and emergency services have been called out to a spree of anti-social behaviour targeting schools in recent weeks, say police.
Investigating officers say that play equipment, air conditioning units and a poly tunnel have all been damaged at local schools.
A police spokesman said: "With the nicer weather, later nights we’ve been having there has been a significant increase in reports of youths climbing onto roofs over the last few weeks, particularly around Duke Street School, Mayfield School and St Gregory’s School.
"Unfortunately whilst trespassing on the school grounds, damage has also been caused to play equipment, air conditioning units and a poly tunnel.
"This type of behaviour will not be tolerated under any circumstances. Not only are the young people involved putting themselves in unnecessary danger, they are tying up valuable police resources and also having a detrimental effect on the schools ability to operate fully.
"If you are a parent, guardian or carer of a young person, can you have a conversation with them about the dangers of climbing onto buildings and strongly discourage them from using the sites as a place to congregate."
A number of youths responsible have been identified in connection with the incident.