This article reports on a study on publicly run schools in the Republic of Trinidad and Tobago which has found that, while single-sex schools may benefit female students who prefer a single-sex environment, they are not inherently beneficial for boys or most girls. While the findings are based on data from one Caribbean nation, experts say they may carry implications for public schools in the United States. Even as single-sex options in U.S. public schools have multiplied in the past decade, both their proponents and detractors point to a dearth of reliable research on the topic. The Trinidad and Tobago study, which set out to fill that gap, runs counter to anecdotal evidence of single-sex programs' successes, but may bolster the cases both of opponents and of advocates who say single-sex schools should be a choice for those they do help. The findings come at a time when single-sex public schooling remains a point of contention in the United States, with the American Civil Liberties Union, for one, contesting individual programs.