As boys in the upper elementary grades become increasingly influenced by peer pressure, many are less likely to participate in singing activities because singing is considered a "feminine" activity. The purpose of this research was to explore if there was an effect on upper elementary boys' level of participation during group singing activities when they attended music classes in a single-sex setting. This study employed a true experimental design and a mixed method. Boys (N = 186) were videotaped during their regular coeducational music classes on two occasions to establish baseline data. Then the students were randomly assigned to attend music classes in either a single-sex or coeducational group. Boys were videotaped again after seven music classes (approximately 9 weeks later). The videos were scored using the author-designed Singing Participation Measure, and the scores (N = 123) were analyzed using an analysis of variance (ANOVA). In addition, qualitative data were collected in the form of music teacher interviews and journal entries. The ANOVA showed no statistically significant differences between groups (single-sex or coeducational) or within groups (baseline scores versus post-treatment scores). In contrast, the qualitative data showed substantial differences in most of the boys' participation in single-sex classes. The teachers reported a sudden increase in the boys' singing participation and described numerous advantages of single-sex music education. Further research is needed. Implications for music educators suggest teachers could create single-sex singing opportunities, choose repertoire mindfully, and establish a "singing culture" at the school to increase boys' participation during singing activities. In addition, music educators are encouraged to know their students' strengths, weaknesses, interests, and needs, and to remember that "one size" does not "fit all" when it comes to what is best for developing young musicians. [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.]