This paper explores how students from three different high schools (one all female, one all male changing to coeducation, and one previously all female, and now coeducational) experience school culture, how institutions, through their policies and practices, communicate normative behavior about gender, and how gender is communicated through aspects of school culture were studied. All three schools were in a large Catholic diocese. Data came from research in the general areas of: (1) school policy and administration; (2) curriculum; (3) pedagogy; (4) student outcomes; (5) school culture; and (6) faculty action research. Classroom observations, student focus groups, surveys of students, and student and faculty interviews were used. In the first year, 225 males were interviewed, and in the second year, 481 males and 178 females completed the survey. Fifteen young women were interviewed before high school entry, and four focus groups were formed. Students experienced different cultural realities when they were in single sex schools than in coeducational schools. The value of femaleness was higher in the all female school than in the coeducational settings, and females in the single sex setting had a higher sense of efficacy and individual power than did females in the coeducational setting. Embedded in the culture of the coeducational institution was the lack of recognition of femaleness, and even its devaluation. In the female system, however, being female was an explicit part of the culture. The coeducational setting that once had been all male emphasized uniformity and obedience to authority, while the all-female setting emphasized individuality and perhaps even encouraged rebellion. Appendixes contain the questionnaires completed before and after coeducation at the previously male school. (Contains 1 table and 31 references.) (SLD)