MOORE, Okla. -- Just before the morning bell, chaos erupted at Plaza Towers Elementary School.
A teacher discovered a loaded gun in his classroom chair, prompting teachers and administrators to issue an immediate lockdown.
About 400 students were kept in the school cafeteria while police scoured the school for other weapons and reviewed school surveillance tape.
Parents, like Pamela Rupert, raced to the school to check on the children.
Rupert said, "They issued a red alert notifying parents of the situation. They said everything was under control but I wanted my daughter out of there."
The school gave parents the option of picking up their kids or allowing them to continue their school day once the threat was eliminated.
About 50 families elected to pull their students out early.
Moore police later confirmed the gun was left behind accidentally.
A teacher was at the school with a relative.
We're told the Smith & Wesson slipped out of the relative's pocket, undetected.
Only after seeing the lockdown on television did the person realize his gun was missing.
The District Attorney will decide if any charges will be filed.