Separating boys and girls is a long-established practice in private schools. In public schools, it is a still-controversial notion that has gotten a foothold in districts across the country in the last decade.

Pittsburgh Public Schools officials have entered the debate with plans to create two such programs at Pittsburgh Westinghouse High School next year in an effort to turn around the persistently low-performing school. The proposal, part of a plan to improve the district's high schools, could come up for a vote as soon as Wednesday.

Proponents argue that single-gender schools can raise self-esteem and improve aptitude, particularly among historically disadvantaged student groups.

Critics, who over the years have included the American Civil Liberties Union and the National Organization for Women, counter that students ought to learn in a diverse environment, with gender as much a part of the equation as race, ethnicity and socioeconomic background.

Derrick Lopez, assistant superintendent for the city's secondary schools, said the proposed Westinghouse concept aims to engage parents and students in a model that has proven itself in the private sphere.

"We see the evidence at schools like Oakland Catholic, Central Catholic or The Ellis School," he said.

The single-gender model is premised on the idea that assigning students of only one sex to a classroom fosters a better learning environment by eliminating social pressures that can affect academic performance.

Under that theory, teachers don't have to deal with distractions created by students trying to navigate the intricate social balance of a coed environment. Students are free to express themselves without worrying about the pressures of impressing the opposite sex.

Detractors argue that the education process includes acquiring social skills needed in the coed world outside the schoolhouse. They say single-gender schools may well foster stereotypes and sexist sentiments about how boys and girls learn and may stunt their social maturity.

Wendy Kaminer, a Boston-based author, social critic and former national board member of the American Civil Liberties Union, contends that the single-gender movement bases its theory "mostly on assumption, hopes and stereotyping about different learning styles."

"They tend to exaggerate achievement results. But the truth is we still don't know that single-gender necessarily creates better schools," she said.

Sara Rose, staff attorney with the ACLU of Pennsylvania, sent a letter to the school board this month citing three issues of concern.

First, she said, it is not clear that sex-segregated public schools are legal under state and federal law. Second, she said, the school district has provided no information to the public about how the schools are going to work.

The third issue the ACLU has, Ms. Rose said, is that research doesn't show that sex-segregated public schools generate better academic performances.

"It doesn't make sense that the city is going to try this experiment on kids," said Ms. Rose, who also spoke on the topic at the board's July 12 meeting. "The school board is voting on something that they don't even have all the details about yet."

Advocates and opponents agree there is no overwhelming evidence that segregating students by gender is a superior model for raising academic achievement.

Leonard Sax, founder of the Exton, Pa.-based National Association for Single Sex Public Education, contends that single-gender schools are not the solution for every troubled school. When they are created merely for the sake of replacing a dysfunctional school with something different, the results are often disastrous, he said.

"Simply saying that it works in private schools is not useful," said Dr. Sax, who has written three books on the subject.

Numerous factors help explain why students flourish at single-gender schools -- especially at private and some public charter schools -- but none is more important than socioeconomic status, he said.

"The kids you'll find at The Ellis School are not representative of the kids coming from low-income neighborhoods," he said. "In private school and in charter schools, you have a selected group of students. They thrive in a culture of achievement that is created by stringent rules and standards. There is little room for error."

Middle-class students whose parents read to them, provided computers in their homes and set high educational goals are likely to thrive in both coed and single-gender schools, Dr. Sax said.

But in public schools, he said, administrators also must contend with the impact of poverty, single-parent households, crime and popular culture, which often fosters the image that academic excellence is not cool and unmasculine for boys.

Successful single-gender public schools must create "a compelling alternative culture" just to compete with those influences, Dr. Sax said. That means establishing a process to select students and training teachers to understand the intricacies of a single-gender environment.

Research in brain development as well as test results show that the single-gender model is most likely to improve academic achievement for elementary students, he said. By the time they hit middle or high school, he said, it may be too late to change bad habits and academic acumen regardless of the type of school.

Pedro Noguera, a professor of education at New York University, contends that raising academic achievement has little to do with school organization, much less gender segregation. Creating an environment that is conducive to learning is what is effective, he said.

"The things to focus on are safe schools, good teachers and mentoring," said Dr. Noguera, author of "City Schools and the American Dream" and other books. "It doesn't matter whether the school is single-gender."

Opponents of gender separation in public schools insist it's a step backward in developing equitable opportunities and fosters age-old gender stereotypes. The result, they said, are girls and boys who have been deprived of a well-balanced education.

"That's my biggest concern," said Annette Werner of Shadyside, whose children attend city schools. "The real danger here is that we create schools that build upon stereotypes like boys are competitive and girls are passive.

"For a woman who came into the professional world at a time when we didn't even have laws against sexual harassment, I am bothered by the message we could be sending to our children -- that they are different somehow," said Ms. Werner, a member of PURE Reform, a watchdog group organized by city parents and taxpayers.

Mr. Lopez, the point man in implementing the school district's five-year plan to reform its high schools, said he agrees with Dr. Sax that middle-class students thrive in both coed and single-gender schools.

A lawyer and former high school teacher at all-boys University of Detroit Jesuit High School, Mr. Lopez said his experience taught him that "for low-income kids of color, a single-gender school model has added value." Teachers in those schools have more time and opportunities to interact with students, and can devote extra attention to academic, discipline and behavioral issues.

Mr. Lopez, also a former principal at coed Berkley High School in suburban Detroit, said the only superior aspect of coed education may be the opportunity it offers boys and girls to develop positive relationships with one another.

"You'll find that most single-gender schools have a partner school of the opposite sex. So it's not like students never get a chance to mix with the opposite sex," he said.

Before opening the proposed academies at Westinghouse, Mr. Lopez said, the district will spend a year educating parents and training teachers about the nuances of a single-gender environment. Students who live in neighborhoods assigned to Westinghouse but who choose not to attend the single-gender academies will have opportunities to attend other district schools, he said.

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