Authorities said a custodian found the body of 25-year-old Roy Alan Craddock of San Bernardino near the flag pole in front of Muscoy Elementary School.
The cause of death has not yet been determined, but it was being investigated as a homicide. Sheriff's deputies say there was trauma to the body, but didn't elaborate.
Deputies say Craddock didn't have any connection to the school.
Officials say classes at the school continued throughout the day without disruption. The area around the investigation was cordoned off, and access was cut off to students.
Anyone with information is urged to call the San Bernardino County Sheriff's Department at (909) 387-8613.