Another shibboleth bites the dust. Have you ever heard (dinner parties?) that girls do better in all girl classes? If so, this is correct – there is indeed such an association. But the observational studies do not compare like with like – the comparison groups are not equivalent since single sex schools tend to have more selective intakes than their controls. So we need within school comparisons or, even better, RCTs. There is one example of each in Hattie’s monumental study (pages 96-97), – Marsh & Rowe  and Signorella, Frieze & Hershey. In both cases there were – wait for it – no advantages for all girl classes on educational attainment or career choices, and in the former study, the point estimates were negative for the brightest girls. Likewise, boys did not perform differently in all-male vs. mixed sex classes.
— Richard Lilford, CLAHRC WM Director
- Hattie J. Visible Learning: A Synthesis of Over 800 Meta-Analyses Relating to Achievement. Oxon, UK: Routledge, 2009.
- Marsh HW, & Rowe KJ. The Effects of Single-Sex and Mixed-Sex Mathematics Classes Within a Coeducational School: A Reanalysis and Comment. Austral J Educ. 1996; 40(2): 147-62.
- Signorella ML, Frieze and Hershey. Single-Sex versus Mixed-Sex Classes and Gender Schemata in Children and Adolescents: A Longitudinal Comparison. Psychol Women Quart. 1996; 20: 599-607.