As a general helmet thread, I wouldn't get into it, but as an instructor, I think there should be a bit of a difference. I require anybody that rides at my farm that is UNDER 18 wear a helmet at all times when mounted. This has more to do with liability than anything else. That said, if any of my students are present, I will ALWAYS wear a helmet. That doesn't mean I always wear one when they aren't around, because I don't. But it falls into the category of responsible trainer and good example. They are learning from me, and if I require a helmet of them, then I should wear one myself. I do not judge anyone else one way of the other. It it up to them what they do, but my facility, my rules.
"Keep a leg on each side and your mind in the middle"