The Executive Heads of Five Islands School have apologised for any disruption caused by their decision to close the school following a power cut on Tuesday.
Some parents were forced to take time off work to look after younger children when they were unexpectedly sent home from school before it started.
In a letter to parents, Venture MAT Executive Heads Sara Davey and Sean Powers said that they "sincerely apologise" for any disruption caused by their response to the outage.
They wrote: "On Tuesday morning, The Five Islands School was faced with an emergency situation as a result of a power cut on St Mary's and St Martins. On arrival at the school at 8 o'clock the senior staff assessed the situation and examined the safety of using the school site when there was no power. It was quickly realised that it was unlikely to be viable to keep the school open for anyone because there was no fire alarm operational or toilet facilities. In addition there was no kitchen or communications systems working.
"We checked with emergency planning in the Council and it was confirmed that students and staff could not remain on the school site without fire alarms. We therefore decided in the interests of safety to close the school and let the parents know of our decision by the best means possible. As no computers were working and no phones were operational we had to rely on the use of mobiles in the first instance. Secondary children were encouraged to phone home and confirm with a member of staff that they were able to go home.
"Mundesley children returned to the boarding house with staff members. Primary pupils and parents were told of the decision at the school gate and any children who had arrived independently to school were asked to return home if they knew parents were still there or at a local place of work.
"We are in the process of doing a full review of our response to this emergency closure and will ensure that a full emergency plan is written to accommodate a similar situation in the future. We will share this plan with you and welcome feedback.
"On reflection, we recognise that sending children home, when parents were not aware that the school was closed must have been very disrupting and disconcerting and we would like to offer sincere apologies for this to any parent that found themselves with an unexpected returning child at home or work.
"Immediate actions will involve ensuring that class teachers and tutors have up to date mobiles numbers on their phones so parents can be contacted quickly in a similar circumstance. If any parents have an unresolved concern the school would be happy to discuss this. We are unable to make professional responses to anonymous comments on Facebook. Once again, we offer sincere apologies for any distress caused."
Hundreds of properties on St Mary's and St Martins were affected by two separate outages during Tuesday.