The teacher cleared a classroom and removed the weapon.
Police say a 17-year-old ninth grade student had five.45 caliber rounds and a bb gun.
Officers said the BB gun resembled a .357 or .40 caliber weapon.
The student was arrested and charged with possession of ammunition by a person prohibited and possession of a dangerous instrument.
No on was harmed.
Students were allowed to return to class. The school was not placed in lockdown.
A Christina School District spokesperson has not yet responded to messages left requesting comment.
