That point should be determined at the discretion of the instructor/owner/Master. Either decision, whether he thinks that having someone ( whether they are disabled or not ) under his tuteledge serves his purposes - whatever they may be - should be his or her call. Thats the ideal. The problem is the large, grey area where you have a somewhat dodgy to begin with instructor who, for whatever reason, agrees to have a person with a disability that really requires instructors who, even if they don't understand the ramifications of a particular disorder, at least they've the heart to want to teach. So he lets someone with a fairly significant disability in and, instead of informing the disabled person that he made an honest mistake and they need to reasses things, he keeps the individual on and lets his dog-pack have a go at the poor soul from time to time - for amusement or indifference. It didn't start out that way or by intent of the instructor, but deteriorates into the sad scene because that is often the way people behave in the dog-pack. Of course, people will leave after some point, but its left its effects - just like it did in the school yard - which is probably why the poor fellow or girl went there to train to begin with.