TRACY -- A wave of bomb threats that hit Tracy high schools in March has racked up big bills for the school district,

On March, 13, 14 and 18, the district was hit with a series of bomb threats -- left on bathroom walls and called in to the schools, that forced evacuations and hours of police time to search Tracy and Kimball as frightened parents picked up their kids.

Trying to avert other threat problems, the Tracy Unified School District has taken new measures to improve security. All told, school officials say disruptions and new security measures have cost the district $101,228 so far.

Bomb threats, like those in Tracy, and those suffered this week in Antioch schools, are disruptive and costly.

To try to stop a future incident, The Tracy district will no longer allow calls from blocked/private numbers to reach area schools or district offices. This change was made after one of the bomb threats for Kimball High was received from a private number.

Callers will now need to unblock their numbers by first dialing *82 on their phone, and then the number they want to reach.

"That (Kimball) bomb threat was made from a private listed number," said Jessica Cardoza, a district spokesperson. "After that incident the school district decided to no longer allow blocked/private numbers to any school or district office. Calls went out to parents over spring break about this and we also put this information up on our website."

During the week of threats, the first two bomb threats were found March 13 in restrooms at Tracy High. Students and staff were evacuated to nearby Lincoln Park and police and bomb sniffing dogs were called in. Students and staff were unable to return to campus to retrieve parked cars until after 8 p.m. that day.

On March 14, a bomb threat for Kimball High was phoned in via a blocked number to the district. Students and staff were evacuated and later that day a note was found on the campus of Tracy High with a bomb threat. Both schools were searched by the dogs.

On Friday, March 15, students at Tracy High arrived on campus only to be directed to the gym because the school was still being searched by dogs.

On Monday, March 18, a bomb threat was found in the boys locker room at Kimball and and students and staff were again evacuated. Parents picking up their children had a two-hour or longer wait to get their kids.

"This had never happened to us before," said Tara Gibbons a Junior at Tracy High.

"It was kind of scary at first. At the park, after we were evacuated that first day, we were lost with all the other students ...Looking back, I think it was handled well by security, faculty and police. I hope it never happens again."

Two juveniles were arrested for the Tracy High threats on March 13. No arrests have been made for the Kimball High chaos. The investigation is still on-going.

The district estimates that nearly 4,000 students were affected by this and 2,600 students were absent from school during that time due to the threats.

"These events caused extreme distress to the students, parents and our staff," said Cardoza, the district spokesperson.