The U.S. Department of Education's office for civil rights has proposed amending the regulations governing Title IX of the Education Amendments of 1972--which prohibits sex discrimination in programs that receive federal money--to allow more flexibility in offering single-sex schools or classes. This article discusses the rapid growth of single-sex schools in the United States. The growth of single-sex public schooling has been especially rapid recently. Since 1996, the Young Women's Leadership Foundation, which aims to create educational options for students in urban public schools, has opened six single-sex schools--five for girls and one for boys. The New York City-based organization has schools in East Harlem and the Bronx, in New York, and in Chicago, Dallas, and Philadelphia.