The fire on 1 January destroyed the nursery and infant classrooms at Coed Eva Primary School.
Seven people from the area have been arrested on suspicion of arson with intent to endanger life and are currently on bail.
Crimestoppers has put up the reward as it is believed that there are local people who hold vital information.
Ian Johnston, Crimestoppers' ambassador for Wales, said: "This arson attack has hit a local community extremely hard with over 200 pupils directly affected by the destruction of their school building."
The reward will only qualify if information passed to Crimestoppers leads directly to an arrest and conviction.
A reward of up to £5,000 is being offered for information following an arson attack on a Torfaen school.