A third boy has been arrested on suspicion of arson, following a shed fire at Carden Primary School last Monday (August 7).
Emergency services were called to Carden Primary School in County Oak Avenue at 7.13pm to reports of a fire in the grounds.
No injuries were reported.
Police launched an investigation into the incident, saying they believed it had been started deliberately.
Two boys, aged 13 and 15, were taken into custody and a third, aged 15, has now also been arrested on suspicion of arson.
As recently as July 18th, the school's staff had shared concerns about intruders, writing on social media:
"Unfortunately we have been being visited by some older children out of school hours.
"We have had some resources damaged already and as we go into the summer holidays it increases our concern of children coming in here to play and breaking things or accidently hurting themselves."
Launching a witness appeal, Sussex Police said many people were believed to have been in the area at the time.
Officers hoped to hear from anyone who was nearby, or who might have witnessed suspicious behaviour.
They would particularly like to speak to anyone who may have captured any relevant CCTV, doorbell, or dash cam footage from the surrounding roads.
Anyone with information is asked to contact police online or by calling 101 quoting serial 1271 of 07/08.
Teenager In Custody On Crawley Attempted Murder Charge
Appeal Following Assault In Hastings
Road Closed As Armed Police Attend Incident In Worthing
Lewes District Council Placed In Planning Special Measures
‘Life-Changing’ Medication For Asthma Patients Now Available In Sussex
Arms Factory Demonstrator Disrupts Brighton & Hove Council Meeting
Patients Forced Into 'Pharmacy Bingo' - As Survey Says Medicine Shortages 'Beyond Critical'
Appeal for information After Man Dies In Hastings Collision
Wealden To Hold National Dementia Action Week This Month
Brighton Food Festival To Be Charged For Mud Bath