I hope you're not using it to forward an agenda of regular password changes, James.
Maybe you are only trying to find those that never ever changed their passwords. something which shouldn't really be possible, as when you create your users you, of course, only give them a temporary password, which they immediately have to change.
However, when working with the youngest students I'd imagine their passwords are static for a few years, and then you'd would want them to change it at least once.
That would easily be accomplished by pushing something like gam update users ou /Students/TheYoungOnes changepasswordatnextlogin, don't you think?