Coeducation has been nearly universal in public schools in the United States during the 20th century. Research conducted in the last decade has questioned the effectiveness of coed schooling with regard to the self-esteem and mathematics achievement of adolescent females. Early research reported that single-sex schools where superior to coeducational schools, yielding higher levels of achievement and a greater sense of self-efficacy. More recent research challenges the methods and interpretation of earlier findings. Studies of student performance in single-sex schools lessens the school effect, attributing gains to family background factors. Current findings do not totally dismiss school effects, as class size and curriculum are seen as important factors effecting female student achievement. Analysis of single-sex classes within coeducational schools reveals improved locus-of-control and more positive feelings for mathematics with modest improvement in mathematics achievement. The literature indicates that a sex segregated school environment is not the most critical variable effecting the mathematics achievement of adolescent females. Contains 57 references. (Author)