That's a great question. My old Chen Tai Chi school conducted background checks -- we had one student who had a thuggish disposition and a background check revealed that he had a history of violence. That student's curriculum was modified. I've never seen any other school do it, but I've come across several students with questionable thuglike tendencies. So in my personal experience, I've only come across one school that conducted background checks and would appropriately modify teaching content for questionable students. IMHO it's something that should happen in every MA school, but I've seen a lot of schools that don't, and continue to teach students who are unable to keep their aggression in check.