Bourne Grammar School has confirmed that it was a bomb threat phone call that caused staff and pupils to be evacuated on Tuesday morning.
A suspicious phone call was received on the morning of October 20 during which an electronic voice stated that a bomb had been planted at the school.
Emergency services, including police and a dog unit, attended the school on South Road and people were evacuated at around 10.45am and all were safe, while the public were advised to avoid the area.
The site was searched again by police in the evening and the school was told by the force that the credibility of the threat is “exceptionally low”.
Headteacher Jonathan Maddox wrote a letter to parents as soon as he was allowed back into the building and the school was closed for the remainder of the day. It reopened as normal on Wednesday, October 21.
In a further letter he confirmed more details about the “day’s dramatic events”.
He said: “On Tuesday morning a telephone call was received at the school’s reception in which an electronic voice – not the voice of a real person – stated that a bomb had been planted at our school.
“The entire school was immediately evacuated and the police called. Very soon we had a number of police and other emergency services on site.
“I regret the fact that it was necessary to require all students to remain outside but, of course, I was bound to follow the advice that I received continuously throughout the day.
“This evening I expect that many will be hungry, perhaps cold and some could be anxious. I have been assured that the credibility of the threat – the source of which has apparently been traced by the police – is exceptionally low.
“Nevertheless police dogs will search the site thoroughly this evening.”
Mr Maddox praised the students and staff, adding: “I very much wish to commend all students for their outstanding behaviour throughout their extraordinary experience.
“They conducted themselves sensibly, following the instructions given and were a credit to themselves.”
A spokesperson for Lincolnshire Police said on Wednesday: “Investigations are still ongoing after the school received a suspicious call. No arrests have been made.”