In my case, it depends upon the AI abilitys. I will usualy let him have the greatest amount of responsibility he can handle, and keep a good eye on him. I may let him work a problem himself with a student, or may not, depends on the circumstances. In dives deeper than 10 meters I will alwais lead and let the assistance close lines, though in shalow water I may let the assistant lead, so I can inspect the groupe from behind (you'll be amazed how many things you can notice while watching a groupe from behind). I also tell the assistant to take a slate with him, write down on it the names of all the students, than during the dive I expect him to write down anything he can notice that needs improvement with the students, or any remarks remarks he has, even for me). I do the same, and after concluding a session I sit with the assistant and we go through our slates (I have another one the same) and I can talk to him about what he saw, explained about things he didnt notice. Sometimes, actualy quite frequently, I learn from that something that I didnt notice. I belive this way he get's the maximum experiance he can from the dive. I also give him comments, n the dive-leader level, as I expect him a certain level of handling during the dive.
Assistants in SSI- I'll write about SSI's assitant, as this is my agency- in SSI it goes- Dive Control Specialist (a nice long term for divemaster), Associate instructor, Instructor.
The Divecon is considered an assistant, and associate instructor, is actualy someone that had an instructor course, but hasn't completed his duties yet.
-SSI accepts only their own.
P.S-
I'm quite an individualist in my teaching methods, so the chances to encounter someone the same are rare. But after all- evry instructor teaches differently.