DALLAS, N.C. – Classes are back in session after a bomb threat forced North Gaston High School to evacuate Wednesday morning.

According to Gaston County Schools, administrators discovered the message inside a girls' bathroom Wednesday and evacuated all students and staff while the school’s resource officer and local police searched the building.

Authorities declared the building safe after a search that lasted about 30 minutes, school officials said. Students and staff were then returned to class and the school is operating on normal schedule.

Parents like Terry Heath are concerned, especially since he says he didn't receive any phone messages from the school.

"It's insane," Heath said. "It shouldn't be going on at all. I mean, these kids, they're kids still and bomb threats? I don't understand what's going on."

The school's resource officer is conducting an investigation of the incident, including the review of surveillance video and interviewing students.