Does it matter if boys and girls are taught in the same classroom? This is a question US policy makers currently have to engage but which is also of interest to European countries where single-sex education has a long history in institutions like e.g. catholic schools.
While advocates claim that single-sex education is beneficial to children most of the advanced arguments are far from being scientifically uncontroversial . While a better learning outcome is usually advanced as the main reason reviews of available studies can not find a significant improvement in outcome if the results are controlled for confounding factors. The main reason for these confounding factors are that many single-sex education schools are private and thus have certain criteria for admittance. Additionally students that can not keep up with the expected learning progression might transfer to other schools. Unfortunately only insufficient data on controlled (i.e. double blind) studies are available. These would include randomly assigning students to either single-sex or coeducational schools regardless of socio-economic background. Even in the rare cases where such observations were possible the results are not clear cut .
Another problem for assessing the effectiveness of single sex education is a possible placebo effect. In Schools were single sex education is introduced as a way to improve student performance teachers and students might be more motivated to achieve the expected results. Furthermore there is no scientific basis to assume that boys and girls need different teaching techniques that would make it necessary to educate them separately.
If the upsides are not clear are there any downsides? The answer is quite possibly yes. Research has shown that children are picking up on the distinction that is drawn between boys and girls and assume that this is an important part of how society works. An assumption that has been shown to lead to more prejudice against the other group . Furthermore the students are deprived of the opportunity to learn how to productively interact with members of the other sex in a professional setting, which they most likely will have to do in their later life. Both of these effects could significantly contribute to the ingraining of sexism in society and adversely affect performance in a mixed sex society.
In conclusion a significant amount of research still needs to be done to clarify what exactly the benefits and drawbacks of single sex education are. This is especially important as with all public policy issues the different education models compete for a limited amount of resources. Additionally the research into this topic is already used in legal cases to decide which path public schools in the United States should be taking .
 Halpern et al., “The Pseudoscience of Single-Sex Schooling”, Science 333,1706 (2011)
 Letters to Science, Science 335, 165 (2012)
 Hilliard and Liben, “Differing Levels of Gender Salience in Preschool Classrooms: Effects on Children’s Gender Attitudes and Intergroup Bias”, Child Development 81, 1787 (2010)
 Eckes and McCall, “The Potential Impact of Social Science Research on Legal Issues Surrounding Single-Sex Classrooms and Schools”, Educational Administration Quaterly, 0013161X13492794 (2013)