I teach my students how to behave, and to use dignity and respect the other person at all times. - that should be covered - as part of chess etiquette.
many of the kids need only a gentle reminder - to use dignity and restraint, in victory and to be gracious in defeat (while resolving privately to study that opening or middlegame position where they made an error and never lose to it again).
besides that, if you rub it in, when you win, the other person will resolve never to let you enjoy that again, and will find the cleverness or resources to whip you the next time....
I wonder how many teachers of chess also teach their young students how to behave properly at the board and how to accept victory and defeat ?
Do you think such things should also be taught ? Why or why not ?