The school roof was still alight at midday Tuesday and there is a risk that the school will be burnt to the ground. Firecrews expect to be there for the rest of the day.
Police are following up witness statements that several youngsters drove a car into the school.
"We don't know how the fire started in the car," says police commander Christina Andersson to news agency TT.
The small school building houses 150 pupils. Rissne school's headteacher Johannes Håll says that the local council is helping find school places in the area for the children when they return from their half-term holidays next week.