The 12-year-old and his friend approached a 16-year-old boy on the school's baseball fields around 5:40 p.m., police Officer Jermaine Thomas said.
The 12-year-old and his friend allegedly demanded personal items from the older boy, threatening the 16-year-old with a knife.
The two suspects eventually punched the 16-year-old multiple times and took his cell phone before fleeing, according to Thomas.
Officers were unable to locate the friend, but found the 12-year-old a few blocks from the high school, Thomas said. The boy was arrested and booked into juvenile hall on suspicion of robbery.
Police recovered evidence, including the knife used in the alleged robbery, Thomas said.
The 12-year-old boy's alleged accomplice has not been identified, and an investigation into the confrontation is ongoing, according to Thomas.
