KANSAS CITY • As part of a broader effort, the American Civil Liberties Union has asked a Missouri school district to stop offering single-gender classes.

The request was made in a letter sent Friday to the Adrian R-III school district, about 50 miles south of Kansas City. The 770-student district began offering single-sex math and communication arts classes this fall to sixth-, seventh- and eighth-graders.

The district said in a written statement that the classes were used on a "voluntary basis in an effort to continue improvement of student learning" and said it is reviewing the ACLU request.

Single-sex classes began proliferating after a U.S. Education Department ruling in 2006, which allows such classes whenever schools think it will improve achievement.

But the ACLU has argued the regulations conflict with the U.S. Constitution and Title IX, a federal law banning sex discrimination in education.

The ACLU has taken some districts to court. This month, the head of Pittsburgh's public schools recommended ending single-gender classes after the ACLU threatened legal action. Last month, the Vermilion Parish School Board in Louisiana agreed to temporarily end single-sex classes at a school, resolving an ACLU lawsuit.

The ACLU said in a written statement that many programs in the Adrian district are based on disputed theories suggesting that boys and girls learn so differently that they need to be taught separately. Doug Bonney, legal director of the ACLU of Kansas and Western Missouri, said a growing body of research disproves that theory.

"There's no question that our schools deserve greater attention and investment, but resources shouldn't be wasted on programs that simply do not work," Bonney said in a written statement. "Quick fixes that segregate our schools based on sex violate the law and disserve our kids. These half-baked programs help nobody."