It's not clear yet if this incident is connected to Tuesday's incidents either. Some of the schools reported receiving the threat via voicemail. A follow-up call was made when the students were allowed to re-enter the building at noon.

Students and staff also were evacuated 70 miles to the north, at Silverlake Elementary in Middletown, and later allowed to return.

According to the Arlington Police Twitter account, the students were sheltering in place as a precaution and were then dismissed from the high school. No state troopers or bomb squads responded to the scene.

■ Sacred Heart Elementary School in Kingston was temporarily evacuated as police investigated a threat. Law enforcement officials searched the building and by 11:30 a.m. students were returning to class. Like all the other schools and threats before it, however, all of the Pennsylvania locations were deemed clear and the threat non-credible.

A bomb threat was received at the Billerica Public Schools on Tuesday. Parents were seen lining up at Teaneck High School to pick up their children after the threats. Parkside reopened later that day after a thorough search, officials said.

While the safety measures are temporary in nature, they could continue if the threats resume, Fernandez said.

Police say three New Hampshire high schools were evacuated due to bomb threats.

Some of the New Jersey schools were threatened with bombs and others with mass shootings, police said.

Police haven't released specifics on what was said in the threats, but both claimed that bombs were in the courthouse.

Two were simultaneously called in Tuesday just minutes before 10 a.m. One bomb threat was made to Butte High School and one to District Court.

Arlington and Groton students were evacuated Tuesday following separate threats to the schools. Police say the problem is that many keep getting away with it. Some companies, they say, can make these robotic calls very hard to trace.

According to local police spokesman an anonymous caller warned the authorities of the possibility of a bomb attack in one of these schools.

The FBI has volunteered to assist in the investigation since the threat included five states.