Fourth in a Six-Part Series

Mark Lauden Crosley describes himself as a "passionate believer" in public education.

The 54-year-old homeowner in San Francisco's Castro district believes it's critical that children of all socioeconomic and racial backgrounds be educated together. The software designer said he has never voted against any education measure in his life.

But, he said, he believes that even the city's best public schools are overcrowded and underfunded. And despite his belief in the importance of public education, he must do what's best for his three daughters -- so he sends them to private schools.

"There's very little in life that's as important to me as my kids' education. It's a sacrifice you make, and it pays off," he said, noting he nonetheless has nagging concerns that his daughters aren't experiencing diversity in their classrooms. "I don't want my kids in an elite, privileged environment where they don't spend time with people who are different from them. ... But that's the reality, and it bothers me."

His twin eighth-graders, Andrea and Danica, go to Katherine Delmar Burke School near Lincoln Park. He sends sophomore Elinor to the Urban School of San Francisco in the Haight.

Crosley and his wife, Claudia Stern, a financial consultant, get some tuition assistance to cover the total bill of about $70,000 a year. But they still must funnel all of their discretionary income into education -- so no fancy vacations, few movie nights, and no dinners out. Despite the belt-tightening, they're convinced they've made the right choice.

Crosley isn't alone in feeling uncomfortable about private schools while choosing them anyway. In San Francisco, families choose private and religious schools in higher proportion than in any other major city in the country.

Last year, 29.3 percent of the city's school-age population went to private or religious schools. About 10 percent of children nationwide and 8.7 percent of those in California attend private or parochial schools. Marin County has the second-highest rate in the state at 18.7 percent, followed by San Mateo at 15.4 percent and Napa at 13.4 percent.

San Francisco families had 107 private and parochial schools to choose from last year, about the same number as public ones. But those choices have narrowed since about 20 years ago, when there were 144 private and religious schools in the city.

Both private and public schools in San Francisco have seen declining enrollment over the past decades. Since 1982, private and religious schools have lost 10 percent of their enrollment, and public schools have lost 5.5 percent. In 1982, San Francisco private schools enrolled 27,190 students; last year, they enrolled 24,398 students.

The tuition-free public school district is required to open its financial books to the public, report test scores at every school, and provide a range of other useful information. It is governed by an elected Board of Education, holds public meetings and is tracked by several media outlets.

Private and parochial schools -- arguably a second, shadow school system in San Francisco -- are not governed by the state and receive no public money. They must provide only the most basic information about themselves, including their address and how many students they enroll, to the state's Department of Education. They are not required to give standardized tests or report their demographic data. In general, they fly under the radar of government officials and the media.

They can also set tuition like any other business sets prices -- marking it as high as they think families will pay. At Urban, where Crosley's three daughters will all go in the fall, tuition costs $26,000 a year.

That money buys a lot. It buys going to school in a gleaming building newly renovated with $9.3 million, much of it contributed by families on top of tuition.

It buys an average class size of 14, a new laptop for every student who walks in the door, many community-service opportunities, a relaxed atmosphere in which students call their teachers by their first names and don't receive letter grades, clubs for everyone from foreign film lovers to bird-watchers, and a graduating class in which almost all students go on to well-respected colleges.

But $26,000 does not buy everything. Several Urban students said on a recent morning that they sometimes wish they had an educational experience beyond what they call the "private school bubble," a bubble populated by other teens from pricey, revered private high schools in San Francisco -- and nobody else.

"It's a lot of rich, white kids," said Marshall Hendrickson, a blonde, blue-eyed junior at Urban, as he lounged on a sofa with classmates during downtime. "I can't imagine it's that much different than a public school group of friends, but there's a boundary. Private school kids don't interact with public school kids."

Junior Zoe Harris nodded, saying, "It's too bad we have to have private schools. Sometimes I regret I've never been to a public school."

Similar angst-filled discussions play out in households across San Francisco every year as families debate whether to send their children to public or private schools.

Families cite a variety of reasons for going the private-school route. Some say they resent that the school district's lottery system does not guarantee them the right to attend the public school of their choice, especially one in their own neighborhood. (The vast majority of families do get one of their top seven public school choices.)

Other families choose private schools because they want a particular program or feature -- such as an emphasis on French or Mandarin, a religious focus or single-sex education. Others say their children will simply receive a better education in private schools, featuring smaller classes, more resources and more attention for their children as opposed to public school teachers having to focus on students who are far behind.

"The best private school is, in my opinion, better than the best public school anywhere," said Pamela Singer, whose daughter, May, attends Convent of the Sacred Heart Elementary. "When you take a group of people who have money and they just pour money into this school, and they're already like-minded because they've chosen to join this club together, it's just going to be elevated."

Other parents told The Chronicle they don't want their children to be around students who wear "saggy pants" or who "curse on Muni" or who may be "rotten apples." A few said they can see big differences between public school students and private school students just by watching them walk in and out of their respective schools.

The National Assessment of Educational Progress, known as the Nation's Report Card, has tracked students' achievement for the past 30 years and has consistently found that private school students outperform their public school counterparts in all categories surveyed: reading, math, science and writing.

However, the report cautions that the results don't mean private schools are better, because they generally serve a wealthier population with fewer students in special education or who are learning English; therefore, higher scores should be expected.

Dan Kelly, a member of the school board that oversees the San Francisco Unified School District, said he has been jeered in meetings for saying there's not a single private high school in San Francisco that's better than Mission High, a public school often dismissed by middle-school families.

"Is a school better because it serves the most prepared, most connected, most well-off students? Does that make it a better school? No," Kelly said.

Kelly, a physician with three adult children, sent one to Urban and the other two to Lowell High, a public school that selects students based on their academic achievement. He said he now regrets ever having opted for a private school.

"The whole private school movement is really a mistake," he said. "Public schools are meant to be fair, and private schools are meant to be exclusive."

John Leiner, admissions director at the private Chinese American International School, said there is obviously inequality between what parents can afford when it comes to children's education, but private schools shouldn't be blamed for the disparity.

"That's America. It's something that we can't fix," he said, noting California's public schools could lure more families of all economic backgrounds if they were better funded -- and that's where parents and educators should direct their focus.

That said, Leiner added that many private schools, including his, are trying to diversify their classes by offering financial aid.

"We try to have as diverse a class as possible -- that would mean race, socioeconomics, single-parent families, adopted children, gay and lesbian parents," he said. "It provides a richness for the school and a richness for the students."

Still, enrollment at the Chinese American International School is just 4 percent Latino and 2 percent African American. The rest of the enrollment at the school, which offers Mandarin immersion, is 50 percent Asian American, 20 percent a mix of Asian and another race, 17 percent white and a smattering of other designations.

The lack of diversity at many private schools irks Crosley, the father whose daughters all attend private schools.

"If you look at the public schools and you look at the private schools, you can tell at a glance which one's which just by looking at the people there," he said. "The only people who could be happy with that situation are people who aspire to great privilege, and I'm not one of them."

His eldest, Elinor, said she loves Urban and expects to go to college and major in art or design. On a recent morning, she and her classmates signed letters to city officials about topics they'd researched -- hers was the importance of sex education -- and walked together to the nearby post office to mail them.

"I'm really lucky to be able to go here, obviously," she said. "It's just the way it turned out, I guess."