Students at Claremont Academy in Chicago and their scores have become a proof point in a broadening argument between adults and institutions over whether single-sex education does more good than harm, or whether it does any good at all. The battle pits the American Civil Liberties Union and women's groups against some who have been frequent allies but are now turning to single-sex classes in a desperate search for ways to close the cavernous and disturbing achievement gaps between black males and other students.