Cardinal Newman High School in Bellshill fell prey to a break-in - after three raiders were seen entering the premises.
A concerned eyewitness contacted police around 3.10am on Sunday, December 29 after spying the trio.
They are believed to have stolen a two figure sum of money and made their getaway in a dark vehicle.
Meanwhile it has emerged that a Bellshill pub was also broken into the night before.
Thieves entered The Coachhouse in Main Street in the early hours of Saturday and stole a consignment of alcohol. Police are now on the hunt for witnesses in regard to both these incidents.
Anyone who can help is asked to contact 101 or call Crimestoppers free and in confidence on 0800 555 111.