Before class this morning at the Bromwell Elementary School in Denver, Colo., principal Jonathan Wolfer conducted his safety checks with extra vigilance.
"I have lost sleep in the last few days unfortunately, just thinking about what could happen," Wolfer said.
As students and administrators across the country react to the recent rash of school shootings, including this week's violence in an Amish schoolhouse in Pennsylvania, students at Passaic High School in New Jersey said they were nervous.
"Wow, imagine if that happens here? Imagine if that happens to me," said Luis Del Toro, a student at Passaic High School.
Education officials in Texas and Atlanta sent principals e-mail and text message reminders to be "particularly vigilant" right now.
The Texas note warned of copycat acts, saying, "As the similarities between the incidents in Bailey, Colo., and Paradise, Pa., demonstrate, acts of violence such as these have the potential to induce others to commit similar acts. We must never let our guard down when it comes to the safety of our students, and we must be particularly vigilant during the times surrounding such incidents, when the potential for copycat acts is at its highest."
At Passaic High School, principal Carlist Creech also passed that message along to his students and staff, reminding them to be on-guard.
Experts on school violence worry that today's heightened alert will die down as the recent attacks fade into memory.
After the Columbine massacre, schools across the country drafted emergency response plans. But now, experts said, many schools devote limited time and resources to improving standardized test scores, which are often how schools are measured.
"That has become the No. 1 priority, and I'm afraid that school security has slipped," said Del Elliot at the University of Colorado at Boulder.
School violence experts also said government funding for surveillance cameras and emergency drills have been cut.
In 2002, the Justice Department's cops-in-schools program had a budget of $180 million. It's now at zero.
Even schools where safety is a high priority said there's only so much they can or should do.
"I want to create a safe learning environment, and I don't know if a safe environment includes barbed wires and metal detectors," said Wolfer.