By contrast at these schools for military kids, behavioral or academic problems can have direct and serious consequences on the parents and end up having the bump into issues with their command. There's going to be an overall greater degree of focus on discipline in the school, as well as the households, and so on. In many ways the most surprising thing is that the overall difference is only about 10%.
EDIT: As mentioned elsewhere, you also know that the parent(s) in these households are going to have minimum of IQ that's higher than the normal minimum since that's a prerequisite for enlistment. So you're getting a rather overt selection bias there.