Students said it was around 10 a.m. Wednesday when they first heard news of the leak.
"They told us on the intercom that there was a gas leak in the school," junior Joshua Camilo told Channel 2's Tom Jones.
Camilo said immediately some students became alarmed. "Plenty of students were alarmed. A lot of students thought it was going to be a bad thing. It really wasn't that serious," he said.
School officials said a school administrator heard a loud bang come from where construction crews are building a new gymnasium.
That's when they realized a two-inch line had ruptured and was releasing gas.
"Immediately when we discovered there was something out of place, out of the norm, we immediately evacuated the building as a precaution," school spokeswoman Cindy Ball said.
The school evacuated the students to the campus annex and to the elementary school across the street.
Student Dexter Mills said just hearing there was gas leak made him nervous.
"I mean somebody could easily ... just a spark could go off and a huge explosion could happen," Mills said.
After Atlanta Gas and Light stopped the leak, crews measured the gas levels, school administrators said.
"They felt that it was ... the levels were low or no levels at all, so they were able to release the school back over to the county," Sharon Webb of the Rockdale County Fire and Rescue Department said.
Students were then allowed to return to class. School officials said their safety plan worked well.
It worked too well according to Joshua Camilo. "They actually were gonna give us an early release but then since they ended up fixing it there was no early release," he said, smiling.
The school said no students suffered any injuries or illness. A couple of students were treated by paramedics after standing out in the heat too long, the school said.
The school officials said they are working to determine what caused the leak.