Three portable cabins were gutted at Christian Brothers School on the Glen Road on Monday night.
Pupils books and course work went up in smoke in the blaze.
Detective Sergeant Melanie McGrory said: “At approximately 9.45pm Police received a report that three Portakabins had been entered and set on fire.
“As a result of the fire the Portakabins were completely destroyed.
“I would appeal to anyone who may have noticed any suspicious activity in the area of who has any information to contact Detectives at Musgrave on the non-emergency number 101.”
SDLP Belfast councillor Tim Attwood said fire damage was caused to a mobile PE room.
“It is outrageous that the hard work of students was also damaged in the fire attack.
“The community will rally around and support the staff and students of this great community college. CBS Glen Road develops fantastic young students every year and the actions of a mindless few will not stop that.”
Witnesses can also call Crimestoppers anonymously on the freephone number 0800 555 111.