The issue with this study is that they can’t control for changes in society over time because the two groups of students evaluated did not attend school at the same time.<p>For instance, maybe the issue is much more mundane. Access to TV increased after 1994, leading to less time spent studying. Or perhaps students spend more time indoors now, leading to less mental development. There are literally countless causes that are impossible to evaluate. Trying to argue that male teachers bring some type of indescribable quality to the school atmosphere seems crazy.