Mr Cooper's home, in Welstead Road, has been cordoned off and according to Mr Setchell, forensic teams are conducting a "lengthy search", which will last for "several days".
Mr Setchell said the risk of anything dangerous being found at the school was incredibly low but he wanted to ensure it was safe for children and staff.
Anton Setchell, the Association of Chief Police Officers' national coordinator for domestic extremism, said a man was arrested in the early hours of Monday morning and was being held at an undisclosed police station.