Gendered schooling is growing in the United States, but little research exists on single-sex classes in public elementary schools. This study sought to find out if single-sex classes in two elementary schools made a difference in boys' reading gains in 2008-2009, as judged by scores on the state's annual literacy test. In one school, boys in the boys' class gained significantly more than boys in the mixed class. In the other school, boys in the boys' class did not gain significantly more or less than boys in the mixed class, but they did gain significantly less than boys in the mixed class on a nationally normed reading test also given by the school. (Contains 5 tables.)