Officers responded about 3:15 a.m. to a report of a suspicious person in the area of 11th Street and Benson Avenue, said Capt. Marcelo Blanco, a spokesman for the Upland Police Department.
"Three officers were involved in the shooting," the department said in a statement. "The suspect had a replica firearm but at the time of the shooting, officers did not know it was a replica."
The wounded suspect, described as being in his late 20s or early 30s, was transported to a hospital for treatment. No officers were injured.
Police later said the suspect was declared dead.
"We could hear the cops telling him to get his hands away from the gun, 'Put your hands up, get your hands away from the gun.' And then there were, like, three or four shots, and then there was another set of an array of gunshots," said witness Stephanie Orellana.
In accordance with protocol, the San Bernardino County Sheriff's Department was assisting police in the investigation of the shooting.
Classes at the school began at 7:30 a.m. as scheduled. The teacher's parking lot was closed as investigators collected evidence at the scene.
Parents can drop off and pick up students in the north driveway of the school by driving on 11th Street from Mountain Avenue, police said.