Josue Rodas, 13, studies a math problem on the electronic chalk board. He's in a same-gender common core math class G. James Gholson Middle School. (Michael S. Williamson/The Washington Post)

The boys huddled in two teams at the front of Charlene Skinner’s class as they mulled over the math problem that flashed on the whiteboard.

“That’s not right,” one boy said.

“It says find the slope,” another boy said, instructing his classmates.

Next door, in Room A114, the girls spent five minutes in Justin Andersson’s science class writing down everything they know about DNA.

When the allotted time was up, Andersson asked the students to share some of what they jotted down. “Nobody’s DNA is alike,” one girl said after raising her hand. “You get it from your parents,” said another.

This is how some lessons are taught at G. James Gholson Middle School in Prince George’s County: boys in one classroom, girls in another.

Gholson is one of a handful of public schools in the Washington region that have single-gender classrooms, a widely debated approach to teaching that is born out of a longtime educational theory that boys and girls learn differently and, in some instances, are better served by being separated for academic instruction.

Advocates argue that separating boys and girls removes distractions and gender biases in the classroom, taking the lead from expensive private schools and boarding schools that have relied on single-gender learning for generations. But opponents say there is little evidence that such separation works, that it can be discriminatory and that it doesn’t properly prepare students for a world that is coed.

Gholson began separating boys and girls four years ago, and now 20 percent of the school’s classes are single-gender. It is among a small but growing number of public schools across the country that have single-gender classrooms. In the 2011-12 school year, approximately 500 public schools in the United States offered single-sex educational opportunities, according to the National Association for Single Sex Public Education. A decade earlier, about a dozen U.S. pubic schools offered single-gender classes.

It’s not very common in the Washington region’s public school systems. In the District, Excel Academy is an all-girls charter school, and in Fairfax County, some high schools offer single-gender personal fitness classes for girls.

Prince George’s County Chief Executive Officer Kevin M. Maxwell said that several schools in Prince George’s teach boys and girls separately and that the approach has potential for a system that is looking for ways to improve.

“I can’t say it’s a cure-all,” Maxwell said. “But I think they provide part of the answer to the work we are doing.”

Ebony Cross, Gholson’s principal, said the school has had annual increases in test scores, which educators there partially attribute to single-gender learning.

“I hear mixed reviews from kids and parents,” Cross said. “But we have shown growth” in testing.

In 2009, 59.9 percent of eighth-graders were proficient in reading on a state assessment test. In 2013, 64.2 percent of eighth-graders were proficient. In 2009, 21.4 percent of eighth-graders were proficient in math, and in 2013, the number rose to 35.3 percent.

The number of single-sex classes increased nationally after the U.S. Department of Education approved regulations for classes and schools under the national No Child Left Behind policy. The American Civil Liberties Union has made several legal challenges to single-sex classes, arguing that separating students by gender is a violation of Title IX, the federal law that prohibits sex discrimination in federally funded educational programs. But the regulations have been upheld, though some schools have dropped single-gender classes in response to the challenges.

Some experts say single-sex classes can break down gender stereotypes, create opportunities for students and improve test scores.

Kathy Piechura-Couture, an education professor at Stetson University in Florida and a board member of the National Association for Single Sex Public Education, said students tend to be more focused on their curriculum and less concerned about impressing or getting attention from the opposite sex. She said girls tend to “dumb themselves down for boys” when they are together in math and science classes.

But a report released last week by the Psychological Bulletin — which reviewed 184 studies to compare the outcomes of learning in single-sex and coed classrooms — raised questions about whether there are any real advantages to single-sex classrooms.

Janet Shibley Hyde, one of the report’s co-authors, said there was no evidence to support the contention that boys do better verbally or that girls improve in math and science when in single-sex settings.

Shibley Hyde, a professor of psychology and gender and women’s studies at the University of Wisconsin at Madison, said she thinks that separating students might not adequately prepare them for college and careers.

“One of the major purposes of school is to prepare students for the adult world, and that world is coed,” Shibley Hyde said. “I think we do a disservice to students by not preparing them for the adult world.”

Piechura-Couture said that some of the country’s most powerful women experienced single-sex education opportunities at private schools and in college and that all families should have the option of sending their children to a school that has single-gender classes, not just those who can afford elite private schools.

“Too often, this is afforded to people of wealth,” she said. “I think it should be offered to all economic levels.”

More than three-quarters of Gholson Middle School’s students qualify for free and reduced-price lunches, an indicator of poverty.

LaShawn James of Landover, whose daughter is a seventh-grade honor student, said she thinks it is a good idea to separate boys from girls. “It allows them to be more focused,” James said. “I noticed that she doesn’t come home with complaints about the class being noisy or disruptive.”

Paradise Kelly, 13, a Gholson eighth-grader, said she didn’t know what to expect from the single-gender classes when she transferred from a charter school in the District this year.

“I didn’t think it was going to work at all, but it did,” Paradise said. “It seemed like it was going to be a lot of drama” with all girls in class, “but it’s not a lot of confusion.”

Paradise said that she can concentrate more without boys in class and that she’s learning more.

Next door in math class, Giovanni Melendez, 14, said there are advantages and disadvantages to separating the boys from the girls: “Males like to impress girls they like. You don’t want to look dumb in front of a girl.”