Police, firefighters and medics responded to a call Saturday night after the wooden stage gave way at Servite High School, an all-boys Catholic school in Anaheim.
Students from nearby Rosary High School, an all-girls sister school, were dancing when the stage buckled. Injuries included broken bones, bruises and scrapes.
The likely cause "at this point looks like too many students and too much weight on the platform stage," Anaheim police Lt. Tim Schmidt told City News Service on Sunday.
Investigators will double-check the school's stage permit to determine if it included a weight restriction or a limit on the number of people who could be on stage, Schmidt said.
About 500 students and parents were in the auditorium at the time of the collapse.
