Parents Scared, Frustrated By School Threats In Mass.

BOSTON (CBS) - Tim Oliveri and his twin daughters admit Tuesday was a tough day. "It's scary and you have to take it serious," Oliveri says.

Their school was one of approximately two dozen districts disrupted by a bomb threat since Friday. In fact, all the schools here in Billerica were affected.

"We found out through a phone call and kids didn't know about it, so it was scary to know that happened and they were still there," mother Julie Hogan said.

In Billerica, the schools were swept by police, deemed safe, and the kids were never sent home. But in other towns like Arlington they were released.

"This is extremely disruptive to our students and very unsettling to students," Arlington Police Chief Fred Ryan said. "We are taking this very seriously."

In fact, the local, state and federal authorities are all taking it very seriously. On Tuesday, there were 15 towns that had similar untraceable threatening calls.

It is becoming a trend angering more than police. "It's definitely frustrating and scary," Hogan said. "It's scary I think about the safety of our kids every day they go to school you wonder if something is going to happen."

From fear to frustration, bogus calls have parents looking for answers.

Oliveri says, "It's obviously a little stressful but you have to take it serious, I have no real answer on how they should solve it."

Police say they don't know where the calls are coming from, but they believe there is a connection. Nothing dangerous was found in any of the schools.