St Mary’s School and nine schools in Sheffield received the threat around 6.30 in the morning of April 14.
It was not thought that the email threatened damage by some who said they had a firearm was genuine, but led St Mary’s to suspend the activities of the nursery.
Since then, a 17 -year -old has been arrested by the South Yorkshire police under suspicion of malicious communications.
It has been released on bail while an investigation continues.
A spokesman for the South Yorkshire police said: “At 6.38 am on Monday (April 14) we recovered a report that a man sent an email to nine schools in Sheffield in which he would have caused damage and was in possession of a firearm.
“We understand that this will be worrying for the parents, the students and the staff of our community and we assure you that immediately after the reports the officers worked to the rhythm and have not found evidence that suggests that the threat is genuine.
“A 17 -year -old boy was arrested under suspicion of malicious communications. He has been released on police bail.
“Our research is still ongoing. If you have any group, talk to your local neighborhood surveillance team, they are there to listen and help where you can.”
