Administrators and teachers walked off the football field at San Pedro High School on Wednesday afternoon, cutting short graduation ceremonies for about 560 seniors and their families and friends.
The reason, school officials said, was heckling, screaming, shouting of obscenities, beach balls and balloons flying through the air, and squirt gun barrages by many in the class.
But some of the graduates and their parents said it was just ordinary youthful exuberance at a great moment in life.
Parent Deborah Rogers said school officials called in the police and barricaded themselves in their offices after calling off the ceremonies.
"I think it was an outrage," said Rogers, whose son, Ted, was among the graduates. "These kids worked so hard to reach this important moment and then they get shafted by the adults."
Assistant Principal Rey Mayoral said police were called in only as a precaution and there were no arrests.
"The seniors signed a letter promising that they would observe the dignity of the occasion," he said. "When the event was disrupted by student rowdiness, a decision was made to terminate the ceremony" about 90 minutes after it began at 2 p.m.
"Most of the kids wanted to behave, but there were a few groups and pockets who wanted to make trouble and they got the rest to participate," Mayoral said. "We pleaded with them to cooperate and keep it a dignified occasion, but they wouldn't listen."
Ted Rogers, student body vice president, said he did not hear any warnings about behavior from school officials during the ceremonies.
"Basically, it was rather sedate for a graduation," he said. "Compared to what I've heard about and seen on television. We were just feeling happy about graduating."
Rogers said he and other student leaders will try to arrange their own graduation ceremonies at a local park next week.
Mayoral said school officials arranged for the seniors to pick up their diplomas at the school gym.