Calls were received at East Millsboro Elementary, Beacon Middle School, Polytech High School, Stanton Middle School and Sunnyside Elementary.
State police are investigating a series of bomb threats against four Delaware schools that took place May 23.
Division spokesman Sgt. Richard Bratz said nothing suspicious or out of the ordinary was found at any of the schools.
The threats were called in within 25 minutes of each other, the first at 11:09 a.m. to the East Millsboro Elementary School, Millsboro.
A second call was received at 11:13 a.m. at the Beacon Middle School in Lewes, a third at 11:22 a.m. at Polytech High School and the fourth at 11:33 a.m. at the Stanton Middle School in Wilmington.
In addition, Smyrna Police are reporting the Sunnyside Elementary School received a bomb threat at 11:15 a.m.
Each call was made by an unknown male, Bratz said, with Smyrna Police Department spokesman Cpl. Brian Donner saying the call appeared to have been automated.
In all instances state police, in some cases aided by other agencies, K-9s and school administrators, searched the buildings, and with the exception of Polytech, all staff and students were allowed to resume classes.
Students at Polytech were dismissed for the day, Bratz said.
It is not known if these threats are related to the series of bomb threats which occurred in February within the state, Bratz said.
Anyone with information about these threats is asked to call Troop 2 Youth Aid Division at 302-834-2620, Troop 3 Youth Aid Division at 302-697-4454 or Troop 4 Youth Aid Division at 302-856-5850.
Information may also be provided by calling Delaware Crime Stoppers at 1-800-TIP-3333, via the Internet at delaware.crimestoppes.com or by sending an anonymous tip by text to 274637 (CRIMES) using the keyword “DSP.”