SAN FRANCISCO (KPIX 5) —  The arched brick halls of San Francisco’s Archbishop Riordan High School are about to undergo a seismic shift – not from an earthquake, but from girls. The school board voted last night to make the all-boys school co-ed.

“There’s not going to be another time in history where we can accept students at all grade levels from another Catholic school,” Riordan President Andrew Currier told KPIX 5.

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The move comes after the all-girls Mercy High School on 19th Avenue announced earlier this month it would be closing its doors after nearly 70 years.

That’s when a lingering thought about taking the school co-ed was kicked into gear. “We think a better long-term solution for young Catholic school students, girls and boys is to come to Riordan,” Currier said. “With the closure of Mercy, there is one less option. Riordan is now open to accepting all students.”

He says the school has enough room to absorb all of the Mercy students who already join in for music and theatre.

The school will need to hire three to four more teachers as well as a dean of women and another counselor.

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Some of the 660 boys at Riordan says it’s a change that will take some getting used to.

“I think at first I was very opposed to it, because it’s sad to see tradition that we’ve held for 70 years,” said student body president Michael Gray. “I felt like it was going down the drain. Upon further inspection, we are maintaining the aspects of our culture that are most vital to our school.”

While girls will be coming on campus, the classrooms will be single sex – either all boys or all girls.

“It’s easier to raise your hand in a classroom that’s surrounded by other males. People would not participate as much if it was co-ed,” Gray said. “So, the fact that we were able to maintain that single gender environment is really important to the transition process.

At least one alum wasn’t thrilled with the thought of a co-ed campus.

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“If you have girls and boys, you can kind of get lost and confused. Education is important,” said class of 1986 alum Jerry Bruno.