Gender differences in mathematics learning continue to attract much research attention. Single-sex settings as the preferred option for improving schooling for girls have evoked fierce advocates as well as critics. This case study, undertaken in response to a specific request from a co-educational state school in the outer area of Melbourne, Australia, and with its maximum cooperation, examined both the shorter and longer term effects on students' attitudes and performance in mathematics of the introduction of single-sex mathematics classes at the grade 10 level. Important dimensions of the study included surveying students in as well as out of the program, seeking the reactions of parents to this initiative, and the opportunity to assess the effect of the introduction of such classes at grade 10 instead of at lower grades (7 and 8), where such interventions have more typically been tried. Results include: (1) Both female students and mothers were more favorably inclined towards the single-sex mathematics program than were their male counterparts; (2) Performance levels for males and females were not significantly different throughout the project year; and (3) Anticipated and actual subject choices for grade 11 were no different for males and females; however, anticipated subject choices for grade 12 showed more differences between males and females than past state average statistics. Contains 10 references. (Author/MKR)