Either way works
I learned on an automatic then my wife made me learn how to drive a standard. I don't particularly like standards but can drive them.
My wife learned on a standard then drove automatic. She prefers standards (except for in stop and go LA traffic).
Both of us drive reasonably well.
Cheers,
Ben
PS A VERY good first exercise - which wouldn't stress you at all to do, is to get him to understand where the blind spots are. Seat him in the driver's seat. Let him adjust mirrors, then with head forward. Then you walk around the car, slowly, having him call out whenever you go in/out of view of . At his call, you stop, let him turn to see exactly where you are, turn his head back to the front, then proceed. When you walk past the side of the car, be sure to be about as far away as the next lane of traffic.
