As shown in the Summary Table, every study falls into one of 
four categories: Pro-SS, Pro-CE, Null, or Mixed. If a study’s findings all supported SS schooling for a given outcome variable, it was coded as “Pro-SS”. If the study’s findings all supported CE for a given outcome variable, it would be coded “Pro-CE”. A study was coded “Null” if for all findings regarding that outcome variable, there were no differences between the SS and CE schools. A study was coded “Mixed” if the study had significant findings in opposite directions for different subgroups on the same variable. For example, a study would be coded “Mixed” if on a specific outcome, support was found for single-sex schooling in the case of boys and support was found for coeducation in the case of girls. If a study had findings that were both pro-SS and null, it was coded a pro-SS; if the study had findings that were both pro-CE and null, it was coded as pro-CE. It should also be kept in mind that some researchers evaluated multiple outcome variables in their research; therefore, it is possible that a single published study would yield information that appears in multiple rows of the Summary Table.
Implications of Review
In general, most studies reported positive effects for SS schools on all-subject achievement tests. Studies examining performance on mathematics, science, English, and social studies achievement tests found similar findings with one caveat. Within each of these subject-specific categories, roughly a third of all studies reported findings favoring SS schools, with the remainder of the studies split between null and mixed results. This minimal to medium support for SS schooling applies to both males and females and in studies pertaining to both elementary and high schools. The overall picture is split between positive findings for SS schooling and no differences or null findings, with little support for CE schooling. The one study that found advantages for CE schooling found advantages for white females but not for Asian or black females. Males continue to be underrepresented in this realm of research.
Another example would be a finding favoring single-sex in a 10th-grade sample and coeducation in a 12th-grade sample for the same outcome variable within a single study
As opposed to concurrent indicators of academic achievement, any positive effects of SS schooling on longer-term indicators of academic achievement are not readily apparent. No differences were found for postsecondary test scores, college graduation rates, or graduate school attendance rates. However, all the findings in this domain came from a pair of studies, indicating the lack of high-quality research on these important criteria. Although some studies favor single-sex education in the case of postsecondary test scores, there is a dearth of recent studies using controls. There has been a similar lack of research on other potential criteria in this domain, such as college grade point average, meritorious scholarships or funding attained, postgraduate licensure test scores, and any career achievement that could ostensibly be tied to quality of schooling.
This category includes a range of outcomes that are not easily grouped together, and the results are mixed. Regarding self-concept and locus of control, the studies are split between those showing positive effects for SS schooling and those showing no differences. In the case of self-esteem, a third of the studies supported CE schooling while half found no difference. Given a recent extensive review concluding that self-esteem’s relationship to school success, occupational success, better relationships, leadership, delinquent behavior, and other desirable outcomes is modest to nonexistent, the implications of findings regarding self-esteem appear complementary. Furthermore, CE schooling only had a positive impact on the self-esteem of males.
