Arleen Forsheit was deep into the intricacies of stoichiometry with her accelerated chemistry class one morning in January when the subject abruptly turned to the president of Harvard. He had said something about how "innate differences" kept women from excelling like men in math and science. "If that's true," one girl asked Dr. Forsheit, "then what are we doing here anyway?" To which the teacher replied, "It's not true."
As a scientist, Dr. Forsheit knew that words, however reassuring, were not enough. A hypothesis needed evidence, an assertion required proof. And what offered more proof than the scene unfolding before her amid the graduated cylinders, gas spigots and molecule models of her own lab. Nearly a dozen ninth graders, every one female, were mastering the mathematics of chemical equations, otherwise known as stoichiometry.
No place in America, perhaps, supplied a more forceful rejoinder to conventional assumptions about women and science than Marlborough School, a private all-female institution for Grades 7 through 12 in Los Angeles. Ninety percent of its 263 upper-school students take more than the two full years of science required for graduation, filling no less than eight physics classes and populating a coveted seminar known as Honors Research. They have gone on to major in sciences at Stanford, U.C.L.A., Yale, Princeton, Johns Hopkins, and, yes, Harvard.
At the same time that Marlborough dashes the thesis of the Harvard president, Lawrence H. Summers, though, it also recognizes that the gender imbalance in the sciences that led to his comments has been real and cannot be wished away with paeans to diversity. In a conscious, deliberate way, Marlborough set about in the last decade to alter its century-old reputation as a stronghold of the arts and humanities - women's work, academically speaking.
"We wanted to establish the expectation that in all ways the bar is high and that our girls can achieve in all areas," said Barbara Wagner, the head of school at Marlborough, who was a music teacher.
Dr. Forsheit put it similarly: "We wanted science to have the same mind share as humanities. We wanted girls to take the extra year of science the way they were already taking the extra year of history or foreign language."
To the task, Marlborough brought the obvious advantages of a well-endowed independent school: small class sizes, lofty admissions standards, wealthy alumni. Still, the school's achievements in science also must be understood as the result of a different factor: There are no boys at Marlborough to dominate, distract or intimidate smart girls.
With a dress code strong on khaki, navy and pleats, Marlborough has also made itself an island apart from the relentlessly materialistic and pervasively sexual popular culture manufactured practically next door by Southern California's entertainment industry.
In the single-sex environment, girls can be girlish and at the same time be brilliant. They can giggle and tug on split ends and speak in those sing-song Valley Girl cadences, all the while discoursing on such personal specialties as cognitive psychology, phytoplankton, Parkinson's disease and mother-infant attachment among gibbons.
"It's assumed every girl will take math and science, not just the special ones," said Jessica Friedland, a 17-year-old senior from Los Angeles who will enter Stanford in the fall. "It's always surprising to people from other schools. You can see the shrugging of the shoulders, the rolling of the eyes. I say, 'Why not take Physics C?' I was never a good speller, anyway."
Having come of age two generations earlier, Dr. Forsheit experienced a fiercer sort of resistance. The sole daughter of a New York truck driver with an eighth-grade education, she was informed by him that she could only attend college if it was free. Fortunately, Brooklyn College met the criteria, and from there she advanced to a master's degree in biology from Columbia, a doctorate in molecular biology from U.C.L.A. and a post-doctoral fellowship from the California Institute of Technology.
Along with diplomas, she collected indignities. A Columbia professor once predicted that she would bomb in physical chemistry. (She got an A.) A brother-in-law said of her Cal Tech position, "You took a job that should've gone to a man." A lack of child care forced her to leave research in the 1970's to raise her two children, both daughters.
ULTIMATELY, she enrolled them in Marlborough, and found her way into a part-time faculty position. At that point, in 1989, only 10 girls in the entire school took physics. When Ms. Wagner was appointed head of school soon after, though, Dr. Forsheit gained a potent ally and advocate in building up the science program.
Out went the traditional "layer-cake" approach to middle-school science - separate yearlong courses in life, earth and physical science - and in came integrated courses that emphasized laboratory work over lectures. During the 1990's, Marlborough raised $7 million to expand and update its science rooms. The number of science faculty members went from 6 to 10, half of them women.
Most important, in the ineffable way of such things, the communal culture of the school changed. High-end science became, well, cool. That was clearest of all in Dr. Forsheit's honors seminar, which pairs about 10 juniors and seniors with an individual mentor from a hospital or research center to conduct research.
Often, the Marlborough girls are six or eight years younger than even the greenest graduate student in the lab. Yet some, like Stephanie Dusaban, have closed much of the knowledge gap over the past year. Her project developing stem cells at the Saban Research Institute in Los Angeles helped persuade Cornell University not only to admit her but also to offer her $8,000 for research - the sort of incentive generally dangled in front of doctoral candidates, not incoming freshmen.
Tomorrow night, Dr. Forsheit's elite students will present their final projects to classmates, faculty members and parents. At Marlborough, the ritual is "the academic equivalent of a debutante ball," as the author Karen Stabiner writes in her 2003 book about single-sex education, "All Girls" (Riverhead Books).
Which does not mean that all of the spectators can fully appreciate the spectacle. "My parents read all of my research papers," said Meryl Holt, a 17-year-old senior choosing between Stanford and Harvard. "And they always say afterward: 'You know, Meryl, that's so great, so well-written. I don't know what a word of it meant.' "