Armed police were called to a secondary school in Lincoln after a report of a youth carrying an air rifle.
St Peter and St Paul Catholic Voluntary Academy was locked down on Monday morning.
The move followed a report of two youths, one of whom was alleged to have been carrying an air rifle, near the school.
The incident at the school on Western Avenue was reported at about 9.30am on Monday.
Armed police were deployed to the scene and a “thorough” search was carried out in the nearby area.
Police said later no weapons were found and no arrests have been made.
In a statement, Lincolnshire Police said there is “no ongoing risk to the public”.
Assistant chief constable Chris Davison said: “We understand this incident may have been very concerning for the pupils at the school, parents and local residents.
“We do not believe there is any ongoing risk to the public.
“We take any reports of this nature extremely seriously and will always deploy specialist trained officers as a precautionary measure.
“Local officers will be in the area throughout the day to offer reassurance to the public and they will be happy to speak with anyone who may have any concerns.
“We would like to thank the public for their support with our inquiries.”
Last month, footage emerged of a man being pinned to the ground after shots were reportedly fired at a college in Crawley, West Sussex.
Watch: Man pinned down at Crawley College