Should boys and girls be in the same classroom? In some countries, a return to single-sex groups within school establishments is a prospect discussed, considered and already put in place because of continued inequity between the sexes. In physical and sports education (PSE), the question of separation of boys and girls in the classroom is widely debated as an important topic at the international level. The objective of this review of the literature is to present a summary of current knowledge about the effect of mixed or non-mixed groups on the training of students, the process of acquiring motor skills, and, at a more general level, the developing of femininity and masculinity in PSE. The article deals with the difficulties posed by mixed groups in PSE, describes numerous inequities between the sexes and the issues that are particular to a context of non-mixed teaching. This is followed by a status report on the work carried out on non-mixed groups in PSE. Finally, due to the limited number of studies on the subject, as well as the heterogeneous, and sometimes contradictory results, research opportunities are proposed, especially on the way gender develops (“doing gender ”) and emerges through student activity in co-educational and single-sex PSE classes. The maintenance of co-educational teaching is debated in the light of inequities between girls and boys in PSE. Teachers in many countries consider single-sex classes to be part of a strategy to promote greater equity between the sexes. A status report on research into the separation of sexes in PSE classes underlines the uncertain nature of the issue, and suggests further investigation of the way gender develops within this context.