Youths are believed to be behind at least £2,000-worth of damage to the roof at Walverden Primary School in Bracewell Street, Nelson, between July 24th and August 5th.
Sgt Shaun Pearson said: “We believe youths have entered the grounds of the school and climbed on to the roof area.
“Not only is people running around on the roof space causing thousands of pounds worth of damage, the people doing it are putting themselves in danger and we would urge anybody with any information to come forward.”