Seeking advice..

My normally well-behaved 4-year-old takes a martial arts class.  For months, the instructors have been allowing him to act like a monster. I have asked them time and time again to please not allow him to act up, only to be met with, "He's only 4.  You expect too much.  He is just being a little kid." I usually sit and watch to keep him manageable, at least.  The instructor's 15-year-old son also helps teach the class and he play fights with my son, allowing my son to hit him.  I have intervened and told Clayton to not hit or kick him (it is a Jiu-Jitsu class, so it is a lot of grappling, no hitting) and the 15-uear-old tells me and my son that it is okay.  I told him that it is not okay.  I am the mother and I don't want him hitting people.  While my 4-year-old's hard as he can hit punch might not hurt someone who is 6' tall and 249 pounds, it may hurt other people and will cause problems in school.  The 150year-old has also told to do things that will get him in trouble in the past because it is funny. 

Now, the instructor has combined the classes for the smaller kids and all of the sudden, they want my son to behave after months of allowing him to basically do whatever he wants until I intervene and make him behave.  The 15-year-old has also decided that he wants to be an adult to my son, instead of the playmate that he has been for several months.  Tuesday, the instructor asked me not to watch the class because my son is paying too much attention to what I allow him to do and not paying attention to them, now that they want to be discipinarians.  I understand the concept, but when I leave, he is really really bad and the instructor seems irritated.  I understand that they need to assert some dominance and gain his respect, but now they are comaplaining because he is not behaving and actually sent him out to find me, so that I could discipline him for whatever he had done, which I really don't know because I was not there. I explained to him that this lack of respect has been going on for several months now and that they can't all of the sudden expect him to do a complete turn around in regards to behaving for them. 

So, after that super long and rambling back story, I am asking for advice about how to make my son behave for someone else, even if I am not there and the person whom he needs to obey is inconsistent about what is allowed and what is not, as well as already having completely lost the respect from my son as a disciplinarian.  I am really at a loss as to how to proceed.  Any suggestions are greatly appreciated, but please do not answer if you are only planning to call me a bad parent or stupid or any other nastiness, or imply any of those things.  :)  TIA