Pupils were placed in lockdown when an intruder entered a school's grounds.
The intruder, who did not make any threats, was seen at Sutton Community Academy, at about 12.30pm , the school said.
Principal David Mackey said all students were safe during the incident, which happened yesterday (July 22).
Mr Mackey said the intruder scaled a large fence at the school, but was located by the senior leadership team, and the lockdown was over within five minutes.
Students were kept in the school until the matter was dealt with before they were allowed to carry on their day, Mr Mackey said.
He added: "The lockdown was over in under five minutes. The intruder entered the school then left the grounds via another exit.
"The lockdown was more precautionary than anything, and the students were brilliant.
"The incident was quickly resolved thanks to the senior leadership team."
A Facebook post to reassure parents said: "All students are safe following an incident today, with an intruder gaining access to the academy grounds.
"Police were called and the academy instigated lockdown procedures as previously rehearsed.
"Student behaviour was exemplary throughout, and the incident was quickly resolved.
Nottinghamshire police have been contacted for comment.