The mathematics achievement and mathematics attitudes of eighth-grade female students attending independent coeducational middle schools were compared with those of students in independent all-girls middle schools. Participants were 467 8th-grade girls from 10 all girls middle schools, 208 girls from 10 independent coeducational middle schools, and 123 11th and 12th grade girls from 2 independent high schools. An attitude questionnaire was completed by all subjects, and achievement test data were obtained. Results from high school students were used to support attitude measures. The only statistically significant difference in mathematics achievement was found for one (higher) level of the Comprehensive Testing Program. Overall, large differences were not found for mathematics achievement quantitative ability or attitude for mathematics for eighth-grade girls in single-sex or coeducational schools. Implications for mathematics education for females are discussed. (Contains 6 tables and 62 references.) (SLD)