Why would you sell your student short by not shutting it down? As a student at ATP we had strict policies that we adhered to and I agree with them. In the pattern only a simulated engine failure was allowed. You went through the procedure and would start pulling the mixture and your hand would get bumped to show they knew you know what you are doing. Even all the DPE's would follow this. If we wanted to shut it down it could be done as long as you were over 3500. One thing that is important to teach when at a SAFE altitude is that you want to make sure you troubleshoot the engine first. An engine providing partial power is still better than no engine (unless it's a prop over speed issue). After we did our troubleshoot check list we would go ahead and secure that engine and than restart it. I spent most of my multi engine training flying on one engine and I am glad I did. Had a real emergency happened with no instructor I think I would of faired pretty well. I also recommend teaching single engine go around's. This is something that ATP (as far as I know) refuses to teach and I think it needs to be done. What happens when you are at 500 ft one day and some creates an incursion and you need to go around? Better to find out you can or can't do it with two engines than only one. Lastly, I think by not shutting down or not teaching it is setting up some one for a potentially life ending failure.