The purpose of this study was to investigate the effects of class type, coeducational or same-sex, on the self-efficacy of middle school girls in a unit of volleyball. Four intact certified physical education specialists from two Middle Schools were used in the study. All of the teachers were female. In two of the classes, students were split out according to gender with males being taught by one instructor and the females being taught by the other instructor. For the coeducational classes, the students were randomly assigned to either of the teachers, with boys and girls evenly divided between the two classes. Essentially two new classes were created at each school. Quantitative and qualitative methods were used for the study. Two questionnaires were administered to the students. Analysis of data from the questionnaire showed the student variables that were measured quantitatively for determining girls' self-efficacy for learning volleyball were found to be significant at the 05 level, favoring girls in single-sex environments. Data from the post-intervention questionnaire and student and teacher interviews were analyzed to provide insight into student preferences for these contexts. It is concluded from the qualitative data that single-sex classes have a more supportive learning environment, and have better conduct than coeducational classes. / Ed. D.