More than 600 San Francisco teachers and classroom aides skipped school Tuesday to extend their Thanksgiving holiday, leaving district officials scrambling to find enough qualified adults to watch over students.

Officials called in every available substitute to cover the open classrooms but fell dozens short, requiring more than 100 central office staff members with teaching credentials to fill in for the day.

Across the San Francisco Unified School District, 432 teachers were absent - that's about 12 percent of the district's 3,700 teachers - with the vast majority calling in sick or taking a personal day. A few were off for bereavement or training, according to district data.

An additional 179 special-education and preschool aides also took the day off. Almost 10 percent of teachers were also absent Monday.

It seems to have been an only-in-San Francisco problem, with teachers in other Bay Area districts reporting to work as usual.

"It does create a sense of frustration when we have these kinds of numbers that happen for no apparent discernible reason other than it's a day before a holiday," said Superintendent Richard Carranza. "Yeah, it's a little disappointing."

On average, about 7 percent of teachers are absent each day, with the rate spiking to about 9 percent most Fridays.

'It's a tricky dilemma'

At John Muir Elementary in the Western Addition, seven of the school's 20 teachers were absent, with five substitutes and one central office worker covering for them. One position, an extra teacher who works with small groups of struggling students, went unfilled for the day, said Principal Christopher Rosenberg.

"It is not a typical day," Rosenberg said, adding that it also wasn't an easy one.

High absentee rates, especially around holidays, aren't unusual, he added.

"It is a tricky dilemma to balance the rights of employees to have personal days and sick days and the need to provide quality education to children every day of our already short school year," Rosenberg said. "I would love for the district and union to come up with a really good long-term systemic solution."

Technically, the teachers and teacher aides had every right to take the day off.

No need to seek permission

Under their labor contract, they get 10 days of leave per year, seven of which can be used as personal days rather than illness.

That means instead of calling in sick, they can schedule the personal days at will - and they don't have to ask permission, said Dennis Kelly, president of the local teachers union, the United Educators of San Francisco.

And there is no cap on the number of teachers who can take any particular day off.

"This is the first time we've been notified there was an issue in any year," Kelly said. "We don't know if there's a sudden spike this year."

Last year, the absentee rate on the Tuesday before Thanksgiving was 9.9 percent - this year it was 11.7 percent - district officials said.

Other districts didn't seem to have the same problem Tuesday.

In Berkeley, there was "nothing out of the ordinary" in terms of the teacher absentee rate, said district spokesman Mark Coplan. In South San Francisco and San Carlos, district officials also reported no unusual absentee rates.

Oakland Unified and several other districts have avoided the potential for a high absentee issue by creating a weeklong holiday for Thanksgiving.

Carranza and Kelly said they will be looking at the issue.

District officials have suggested a change to the school calendar so students and teachers get the whole week off - a schedule increasingly common in districts up and down California.

"My concern is over what quality of instruction are kids getting today," San Francisco school board President Rachel Norton said Tuesday morning. "If it's too much to expect people to work during this abbreviated week, maybe we need to look at changing the calendar."