A young mother came to sign up for night classes at South Philadelphia High School Thursday with a semi-automatic handgun in her diaper bag, according to police.
The woman told police she didn't realize the gun was in her bag.
Authorities say no students or faculty were ever in danger.
"There was no danger whatsoever," said Philadelphia School District spokesman Fernando Gallard.
Kelly Jones, 21, allegedly walked into the school with her son and another relative around 10:45 a.m. During normal security screening, a security officer saw what appeared to be a gun, according to Police Captain Laurence Nodiff.
When her bag was thoroughly searched, authorities found a .40-caliber Smith & Wesson semi-automatic handgun, police said.
"The security measures worked well," Nodiff said. The school police officers did their job and stopped the threat right at the front door."
Nodiff says Jones, who lives on the 2500 block of S 69th Street, doesn't have a permit to carry a firearm and that the serial number on weapon "had been obliterated." She faces four charges including having a weapon on school property and other weapons charges.
Police say that Jones is no stranger to law enforcement and has a history of assault charges.
Her infant was turned over to the Jones' aunt, police said.
Students NBC10 spoke to say they didn't even hear about the incident and that they feel safe in the school.