In the past few months, dozens of schools have seen widespread absenteeism as students use text messages to warn one another. In April alone:

•More than two-thirds of students took a day off April 21 at two high schools in Maury County, Tenn., after threats that came after the funerals of two murdered young people.

•One-third of students at George Rogers Clark High School in Winchester, Ky., left school April 21 after text messages warned that a student would bring a gun to school.

•Nearly a fourth of students at Tokay High in Lodi, Calif., stayed home April 16 after text warnings of a gang shooting.

Ken Trump, president of National School Safety and Security Services, lists 28 such cases this school year on his website, schoolsecurity.org. He says nearly all the threats turn out to be hoaxes. "Nine out of 10 of these threats may turn out to be unfounded," he says. "But no school administrator wants to be No. 10."

Threats spread like wildfire with cellphones, he says, meaning "Mom finds out about it faster than the superintendent, the school board or even the building principal."

In Fort Wayne, Ind., after a rash of off-campus homicides over spring break, rumors spread of more violence once schools reopened. Students began texting one another, urging classmates to stay home.

"It was just getting psycho," says security director John Weicker, who called a Sunday meeting with administrators, school police and law enforcement. School went on; most kids showed up. "You must respond," he says, "but you have to use common sense."

At New Smyrna Beach (Fla.) High School, a threatening message scrawled on a bathroom wall got the texting rumor mill started: "If you thought Columbine was bad, wait until May 2."

Principal Carol Kelley called police, who quickly learned that the message was an idle threat by a bored student. Kelley called a school assembly, talked to students individually and sent an automated phone message to students' homes to get parents to disregard the threat.

A few students took it in stride, she says: They've promised to show up today wearing T-shirts that say "I survived May 2." But Friday morning, Kelley says, two-thirds of her 1,900 students were absent.

"Some were afraid, and some are on the beach," she says. "And some who were afraid are on the beach."