"The teacher accidentally discharged his firearm during a lesson while it was pointed at the ceiling. Debris from the ceiling then fell," according to a statement by the Monterey Peninsula Unified School District issued to parents of students in the classroom.
A 17-year-old student was struck in the neck by debris, according to his father, Fermin Gonzales III, who spoke to Monterey County Weekly.
"Debris or fragmentation" from the ceiling struck him, according to Seaside Police Chief Abdul Pridgen, as quoted by the paper.
"He was going to go to his next class, but he was pulling out metal fragments," Gonzales said of his son. "It was a soft metal."
"Nobody from the office came in and looked at what had happened," he alleged.
A total of three students were injured.
Firearms are prohibited on school properties by California law, and a statement by Seaside High School says that Monterey Peninsula Unified School District's Board of Education policy "prohibits any person other than authorized law enforcement or security personnel from possessing weapons."
Reserve police officers in California are required to complete at least 400 hours of field training, including learning how to properly handle a firearm.
Monterey Peninsula Unified School District Superintendent Daniel Diffenbaugh said Alexander was not authorized by the school district to carry a firearm, according to the local paper.
Arming teachers as a preventative mechanism against school shootings has been at the forefront of national discourse in the wake of the Parkland shootings.
At a White House meeting with families who have suffered from school shootings, President Trump suggested that arming teachers would deter attackers.
In a series of tweets, he said, "20% of teachers, a lot, would now be able to ... immediately fire back if a savage sicko came to a school with bad intentions ... Far more assets at much less cost than guards. A 'gun free' school is a magnet for bad people. ATTACKS WOULD END!"