Establishing single sex classes within co-educational sites is an option that schools are again exploring. To date Australia has experienced three waves of interest in establishing single sex classes, the first focused on equitable education opportunities for girls, the second centered on boys' literacy and engagement and this current wave focuses on perceived difference between the sexes in co-educational classrooms. With the intersection of middle schooling movement, focusing on learner centered classrooms and current educational agendas aimed at improving student performance and measurable learning outcomes, it is understandable that schools are exploring such student grouping options. However, after thirty years of international research into the efficacy of single sex classes in co-educational settings, the results still remain unclear. This paper navigates the 'muddy waters' of this body of research and suggests a framework to help guide school communities through the decision-making process associated with considering single sex classes.