"On your lefty shooter, make SURE you do a master-eye test on him. If he is actually a right master-eye, he must be re-taught to shoot righty. Since there are almost ZERO true lefty pistols, and only ONE lefty revolver (Charter Arms .38), it's damn hard to get REALLY good as a lefty shooting righty guns. To do that test, get a quarter-size washer out of your collection, and have him hold it out at arms length IN HIS LEFT FIST and "sight" with it on your nose while you observe his eye travel (nystagmus) WITH BOTH EYES OPEN. If he is using his right eye to sight with, it will be apparent. Have him switch to his right hand to confirm. YOU can practice this in the mirror to see what it will look like, just be aware that you are seeing the reverse image of what is actually there and you have to get your mind around that reverse image. Also, that DAO plastic-fantastic he bought is probably like most of the Glock-patent guns and will be VERY sensitive to limp-wristing, promoting several times more chance of misfires than he would have with a JMB-patent weapon (PBUH!). I've heard of (expensive) mods being made to JMB-patent weapons to make sure that they eject directly to the side instead of backwards.
BTW, some say that it is actually dangerous for a lefty to shoot a righty pistol, and the worst of them would be the .45, due to the weight of it's spent hulls. If he gets one directly in the eye, open end first, it WILL ruin his eye. So, you say, I make him wear eye protection. Good. Now let's say he doesn't normally wear eyeglasses, and he is carrying and has to shoot for self defense....
BTW, all that hot gas, powder particles, etc impacting his face and spent hulls whizzing past his face are probably the reason that he's such a poor shot. YOU would have a hard time shooting in that environment. If he is a TRUE lefty (as opposed to a true righty and a TAUGHT lefty), I'd abandon any idea of teaching him with a DA pistol. Send him to the gun shop and have him order one of the Charter Arms Lefty's and teach him how to use that .38 properly as a lefty (for reloads, etc). If he is a TRUE lefty, he will amaze you with how fast he picks up competent gunning with that little revolver. BTW, that gun is very light, has an AL frame, so don't have him shoot a lot of +P in it. Tell him to reserve the +P shells for defense (Box of 20, use 5 in the gun, 10 for reloads, and shoot the other five for familiarization, RAPID FIRE at under 21 feet). "