Controversy surrounds the issue of single-gender education, with advocates debating that the initiative decreases discrimination, improves educational experiences for males and females, and provides parents more choice. Opponents argue that single-gender education is a form of segregation and negates the gains that women have achieved in the area of equality. The purpose of this study was to determine the effects of male and female single-gender instruction on eighth-grade students in the areas of science achievement, classroom discourse, self-concept, and perception, when compared to a mixed-gender class. Findings revealed that single-gender classrooms support mixed-gender instruction for females; males preferred single-gender classrooms, achieved better, and grew in science self-concept. Achievement gains in science were higher in the male single-gender classroom. Discourse analysis indicated that females spoke less often in the single-gender classroom and students displayed more abstract utterances in the mixed-gender classroom. Self-concept was negatively affected by single-gender instruction for females but positively for males. Male and female perception was positive concerning single-gender instruction.