Emergency services were called to Stafford County Junior School, Ringwood Road, around 7.20pm on Sunday (November 15) following reports of smoke coming from the property.
The fire caused substantial damage to the school building, but fortunately nobody was injured.
The cause of the fire is thought to be deliberate and on Thursday (November 26), a 31-year-old man from Eastbourne was arrested on suspicion of arson. He remains in custody for questioning at this time.
Investigating officer DC Jon Moore said: “The investigation is moving at pace as we try to piece together the evidence in this case. We will share what we can when we are in a position to do so, but in the meantime I would like to reassure the community that we are doing everything we can to solve the case.”
Inspector Rachel Barrow from the local Neighbourhood Policing Team added: “This type of offence is extremely serious and we recognise that it has had a significant disruption on the staff and children at the school and the surrounding area.
“We are working closely with the fire service and the school to ensure that we are able to respond to and recognise the wider impact of the fire.
“Deliberate fires in Eastbourne are a real concern and are a priority for both Sussex Police and East Sussex Fire and Rescue Service, to ensure we do everything we can to reduce the risk associated with this crime.
“We are grateful for all the help and support we have received so far with our enquiries, and we continue to ask anyone with any information about what happened to get in touch.”
Members of the public can get in touch with police online or by calling 101 quoting serial 1157 of 15/11.