Greene County is set to become what is believed to be the first school district in the nation to go entirely single-sex, with boys and girls in separate classrooms - a move born of desperation over years of poor test scores, soaring dropout rates, and high numbers of teenage pregnancies.

"At the rate we're moving, we're never going to catch up," Superintendent Shawn McCollough told parents in an impassioned speech last week. "If we're going to take some steps, let's take some big steps."

This pine-shrouded county of about 14,400 people between Atlanta and Augusta has in recent years become a magnet for retirees moving into luxury developments along the shore of Lake Oconee. But the vast majority of longtime residents - and most of the 2,000 students in the county's schools - are black and working class.

McCollough pointed to research showing that boys and girls learn differently, and said separating them would allow teachers to tailor their lessons. Also, boys won't misbehave as much because they will no longer be trying to impress the girls, and the girls will be more likely to speak up in class because they won't be afraid to look smart in front of the boys, he said.

The school board's move to overhaul the system next fall has angered parents, students and teachers, who say they were not consulted. And one of the nation's foremost proponents of single-sex education warned that the board had gone too far.

Leonard Sax, head of the National Association for Single Sex Public Education, said that while single-sex schools and classrooms were rising, he knew of no other community that had converted its entire school system. He called the move illegal.

Federal law allows single-sex classrooms or schools, but parents must also have the option of publicly funded coeducation for their children, Sax said.

"This is the worst kind of publicity for our movement," he said. "It misses the whole point. Our movement is about choice. One size does not fit all. Even a small school district needs to provide choice."

U.S. Education Department spokeswoman Samara Yudof said officials "do not have sufficient facts to determine if the district would be in compliance" with federal law.

Districts across the country have been switching to single-sex education since federal officials issued rules to ease the process in 2006. Nationally, at least 366 public schools are either entirely single-sex or have single-sex classrooms, Sax said.

In Greene County, boys and girls will be in separate classrooms in the elementary schools. Boys and girls in grades seven through 12 will attend separate schools.

McCollough said he hoped single-sex classes would raise test scores and graduation rates in a district where more than three-quarters of the students are eligible for free or reduced-price lunches.

Sixty-seven percent of Greene County ninth graders go on to receive a diploma, compared with 72 percent statewide. The high school has been ranked 332d out of 369 in Georgia.

Research shows that when boys and girls are separated, each group performs better in school and is more likely to go to college, said Julie Ancis, a professor in Georgia State University's school of education.

But she said single-sex schools tended to be private institutions with updated technology and ample resources, not poor school systems like Greene County's.