Corona del Mar High School lost power and phone service for about six hours Monday afternoon, according to the school district.
The campus' electricity went out at 12:49 p.m., according to a statement on the school's website.
CdM's backup generators sustained power for about an hour before stopping, said Newport-Mesa Unified School District spokeswoman Laura Boss.
Students were dismissed at the usual time, 3 p.m., Boss added.
The problem was isolated to the campus.
Southern California Edison was unaware of any problem with power delivery.
"We had no indication of any interruption in Newport Beach," spokeswoman Susan Cox said.
Maintenance personnel made repairs Monday and restored power to most of campus by about 7 p.m., according to school officials.
"Power is back on, with a few exceptions in the portables and 500 building," a statement on CdM's website read Tuesday.
Lincoln Elementary School, also in Newport Beach, lost power last week. That outage lasted for the entire school day Friday but was part of a larger interruption, according to Edison.
— Jeremiah Dobruck