The American Civil Liberties Union is threatening legal action against as many as a dozen school districts from Maine to Mississippi unless they stop programs the group says illegally segregate boys and girls into single-sex classes and promote stereotypes.
The group also was demanding that Florida's Department of Education launch an investigation into widespread single-sex teaching in that state, where 32 schools in 16 districts offer single-gender classes. A spokeswoman for the department said they had not yet received the demand, which is posted on the ACLU's website.
Single-sex education has expanded into as many as 300 public schools in recent years - helped in part by a 2006 decision by the U.S. Department of Education that relaxed restrictions on the practice.
That decision, under President George W. Bush, allowed schools to offer voluntary single-sex classes so long as programs did not violate Title IX, a federal law that outlawed gender discrimination in education.
"Many of the programs rely on faulty theories about the supposed developmental differences between boys' and girls' brains that amount to nothing more than sex stereotypes," Galen Sherwin, a staff attorney with the ACLU's women's rights project in New York, told Reuters.
"We believe that is legally problematic and not supported by sound educational research," Sherwin said.
Proponents of single-sex education, including author and psychologist Leonard Sax say segregating boys and girls can benefit both groups because of subtle differences in the way they learn.
Girls may show increased interest in "non-traditional" subjects such as math, computer science and physics in a single-sex environment, while boys improve skills reading, art and music, proponents say.
Research on the benefits of single-sex education has been mixed. A study published in the journal Science in September said that supposed benefits to single-sex education were "often justified by weak, cherry-picked, or misconstrued scientific claims rather than by valid scientific evidence."
A separate study released this year by researchers at the University of Pennsylvania of high school students in South Korea who were randomly assigned to either single-sex or co-educational high schools found that attending all-boys or all-girls schools was associated with higher language test scores.
Last year a school district in Vermilion Parish, Louisiana, agreed to suspend offering sex-segregated classes until 2016 after a two-year legal tussle with the ACLU over the practice.
In November, Pittsburgh's school district agreed to drop sex-segregated classes at a high school after the ACLU threatened to file a complaint with the U.S. Department of Education.
David Theoharides, superintendent of the Sanford School Department in Maine, described the ACLU's threat to sue his district as misguided.
"Girls tend to read more and boys don't," said Theoharides. "In a science classroom I'd always see boys with their hands up first and being more assertive and the girls being more thoughtful," he said.
Sanford offers optional all-boys and all-girls classes to fifth and six graders, which have proven popular with students, teachers and parents, he said.
"We follow all the state rules and regulations," Theoharides said. "As long as our kids are being successful and thriving we will do anything to keep that going."
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