Chris,
I always start tail dragger students out on grass, if it is available. The airplane is more stable and tracks better. (better in a ground loop also) I find it easier on the student also as the plane is not as squirly as on pavement. With that said, you have to use what you have available.
I also look for mostly calm winds to start with so that the student can learn how the airplane flies without too much outside influence. That too ,may not be possible depending on where you live and the season.
I don't teach primary anymore ,just do flight reviews for friends mainly. Right now I am doing some fill in instruction for another guy on vacation.
Wannafly,
I too have the "fat tires" and love them. I carry 10 lbs of air pressure. When I first taxied out after installing them, I started laughing cause I was bouncing up and down on our grass runway and was only doing about 5 mph ! They are a hoot ! I am used to them now .They have been installed for a couple of years.
Dick