This research contributes to a body of literature that looks for effective responses to the gendered performance gap, the research into the effects of single-sex education, and the social construction of masculinities. This qualitative inquiry focuses on a bounded group of male students who graduated from New England single-sex high schools and matriculated into Boston-area colleges and universities. While there have been a few studies that have examined men as men within the context of higher education, none have explored explicitly graduates of boys' schools or their conceptualizations of masculinities. This qualitative phenomenological study examines the gendered socialization that occurs within single-sex secondary schools and the socio-cultural forces that impact the conceptualizations of masculinities that male graduates' have and the anticipated threats that these men feel in regard to their prior gender socialization upon entering a coeducational postsecondary institution. This study answers the following questions: (1) What are the conceptualizations of masculinities with which male student graduates of single-sex high schools enter coeducational postsecondary institutions? (2) What forces in boys' schools shape students' conceptualizations of masculinities? (3) Upon entering coeducational colleges and universities, what do graduates of boys' schools anticipate will be threats to their prior gender socialization? This research adds to the literature that provides positive representation of men and an alternative to the deficit narrative prevalent in much of the research into the lives of boys and men. This study has implications for parents, secondary and postsecondary educators. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]