MADISON, Wis. -

The American Civil Liberties Union has asked federal education officials to investigate whether three Wisconsin schools legally separated boys and girls into single-sex classes.

The ACLU filed complaints Thursday with the U.S. Department of Education's civil rights office in Chicago alleging a Barron middle school and two Beloit elementary schools violated state and federal law by forcing students into single-sex classes.

A message left with the Barron school district wasn't immediately returned. A Beloit school district spokeswoman says the curriculum is the same for single-sex classes and parents can choose to place their children in them.

The ACLU has targeted dozens of public schools across the country that offer same-sex classes, contending the classes conflict with the U.S. Constitution and Title IX, a federal law banning sex discrimination in education.