Fashion
As appearance is so important for a child's development and making friends, it makes sense that some knowledge of fashion should be passed on through school. Even skills such as how to tie a bow tie are infrequently needed but seldom taught.
Comparing appearance with social interaction (such as having shined shoes and well ironed clothes at a job interview) may encourage children to pay attention to fashion and encourage them to actively reconsider manners and social awareness for any given scenario.