Arsonists torched The Hill Primary School at Thurnscoe this week gutting two rooms and the roof.
Most of the Brunswick Street school was expected to still be closed today (Thursday), after fireraisers struck at around 11.20pm on Tuesday night.
The fire is believed to have started in a shed close to the nursery.
It destroyed two rooms and reached the roof void above the scool, a fire service spokeswoman said yesterday.
Fire crews from Dearne, South Elmsall and Adwick-le-Street stations battled through the night to save the remainder of the building.
Working from a mobile command centre, they managed to put the flames out, and left the scene by 2.45am.
The spokeswoman added: “They did a fantastic job to stop the rest of the school being destroyed.”
A spokesman for Barnsley Council said yesterday that the school was closed until further notice.
He added that the nursery and Hill Top Day Care Centre were also affected, but that parts of the school may re-open this week.