I just got back from taking some family for their first 4-day handgun class. My wife and I did a lot of dry practice leading up to the class and we were both able to get DG. She shot 6 points down (shanked two of the designated headshots into the teeth), I shot 3 points down and missed 0 down by 1 inch (shanked one headshot a little low).
The major keys to making the shots is lots of perfect dry practice and a lightning fast presentation. If you can get the gun out there fast it seems like you have all the time in the world to make the shots. When our rangemaster spent a few relays with me coaching me on the this, I was shocked by how fast the gun came out. I sat there for a good 2 seconds before I took the shot, utterly amazed by the seemingly instant effect of the gun in my hand.
My 3 points down from the low headshot came from seeing a perfect sight picture and alignment and thinking "Now!" in my brain and mashing the trigger.