PHILADELPHIA - A gun found inside a preparatory school has prompted a lockdown in Philadelphia's Frankford section Tuesday morning.The First Philadelphia Preparatory Charter School on the 4300 block of Talcony Street is currently under lockdown.Police say a parent got a call from her daughter about a student with a gun inside the school.A gun was recovered in a student's backpack, then the school was placed on lockdown, according to authorities.Police have yet to release further details about the student or recovery of the gun.This is a developing story.