On-Alert After Littleton

There have been 30 bomb scares, threatening notes and phone calls in Yonkers, N.Y., since the tragedy in Littleton, Colo., reports CBS News Correspondent Diana Olick.

Each time, school officials call out the dogs and scour the schools. So far, they have found nothing.

"WeÂ've had a few bomb scares, people calling in so they have to evacuate the school, send us out to the bleachers for awhile," said high school senior William Geoghegan.

"Right now, we got projects due thatÂ's for our graduation, and we keep stalling, because thatÂ's the time it happened, so weÂ're losing days," said senior Oscar Perla.

"One thing you canÂ't do is stop doing what youÂ're supposed to do," one school official told CBS News. "You donÂ't stop having school because of this. You donÂ't want the people who are doing this to feel that theyÂ've won."

Most school officials will agree — the more shootings and bombings kids see on TV, the more likely they are to imitate. But there is another side. More students now than ever before are watching and listening and turning in their classmates.

Yonkers school district now has a free hot line, no names asked, and it has led to the arrest of two students already.

But the threats keep coming, and the emergency bells keep ringing. In between, students are just trying to get their final work done.