St Mary’s School and nine schools in Sheffield were sent the threat around 6.30am on April 14.
The email threatening harm by someone who said they had a firearm was not thought to be genuine, but led St Mary’s to suspend nursery activities.
A 17-year-old has since been arrested by South Yorkshire Police on suspicion of malicious communications.
He has been released on bail while an investigation continues.
A South Yorkshire Police spokesperson said: “At 6.38am on Monday (14 April) we received a report that a male sent an email to nine schools across Sheffield in which he threatened he would cause harm and was in possession of a firearm.
“We understand that this will be concerning for parents, pupils and staff in our community and reassure you that immediately following the reports officers worked at pace and have found no evidence to suggest the threat is genuine.
“A 17-year-old boy has been arrested on suspicion of malicious communications. He has been released on police bail.
“Our investigation remains on-going. If you have any concerns, please speak to your local neighbourhood policing team, there are there to listen and help where they can.”
