Girls and boys agree on one thing - they don't want each other around in class. Tim Cornwell reports
The war between the sexes flourishes in an all-girls' maths and science class on the second floor of a San Francisco state school. Sarah Wilson, Anny Chounlamay, and Khaledah Wright, all 13, happily explain why they do not want boys around.
"They throw spitballs and stuff like that," said Sarah. "You can learn better without them."
Khaledah said: "You can see the results in my tests, and in my grades. Before I wasn't doing very well. Girls are more mature than boys, it's kind of quieter here than it would be with boys."
The story is the same - though less vocally expressed - in an all-boys' room down the stairs. "There's no girls in here to like mess up your concentration, " said Benjamen Neely, also 13.
If their opinions sound well-rehearsed, it is hardly surprising. The children know they are part of something special. They are involved in an experiment in single-sex education at the Marina Middle School, where a $500,000 (Pounds 300,000) grant has helped fund separate classes for boys and girls in three grades.
Education statisticians from the University of California at Berkeley are frequently in class, struggling to put figures on the knotty question of whether girls perform better without boys, and vice versa. Pupils and teachers have been grilled by a string of education reporters - from the New York Times to Time magazine - asking the same question.
Single-sex education still exists in the US, at religious and private schools. But it is virtually unheard of in state-funded schools. While US courts banned schools segregated by race, they also frowned on those segregated by sex. The presumption has been that where boys and girls were separated, boys would get the lion's share of resources and attention.
That position is changing. The experiment in Marina and a handful of other California schools with single-sex classes fits a current pattern in American education reform of returning to the standards of yesteryear, amid a sense that state schools are failing badly.
Supporters also say they may help young teenage girls, at a period of their lives when they are said to be insecure and lacking confidence, and vulnerable to low self-esteem and eating disorders like anorexia. US studies suggest that while girls equal or outperform boys until they reach adolescence, they then fall behind, particularly in maths and science.
The pilot programme at Marina middle school was directly inspired by a survey from the American Association of University Women in 1992, showing girls got left out in co-educational classes, with boys called on more often.
Most of the 800 pupils at the school are still taught in co-educational classes. But those who sign the necessary papers are placed in the Arthur Ashe Academy for Boys, named after the black tennis player, or the Sally Ride Academy for Girls, named after America's first woman astronaut.
In the school's huge 1930s building, they function as a school within a school. Girls and boys merge for elective classes such as home economics and for meals and play, though not for gym. School administrators say the new option offers parents a choice which they would previously have had to pay for.
The school has drawn two Muslim girls who were taught at home rather than with boys. Several other pupils said their parents had encouraged them to sign up to avoid the distractions of the opposite sex, but others said they took the initiative to be with friends.
As this is San Francisco - a liberal city whose gay and lesbian communities are a powerful cultural and political influence - there seems little danger that boys and girls will fall into sexual stereotypes. The boys are being taught women's history.
The success of the programme will depend on whether it is shown that single-sex education helps - even if only for certain pupils. Teaching staff at Marina say they are still waiting for results, but expect them to be favourable. Several report that boys and girls, alone, seem more willing to take risks and make mistakes. "The quiet girls became a little more vocal, which was good," said Louis DeZutti, a school counsellor, who taught last year. "Some of them became genuine loudmouths, and they still are, I'm proud to say."
In a school that presents a typical Californian ethnic melange - with 44 per cent of pupils of Chinese descent, a third Latino and African American, and the rest everything from Japanese to Russian - one teacher believes the division by sex has helped reduce racial cliques. Another counsellor cites a girl, who was almost mute, but has now read aloud in class - twice.