CraigJ00:
I have hunted SD for many years and took my 13 yr old son for his first hunt there a couple years ago. He is now 15 and eagerly looking forward to going this year for a week around Thanksgiving. Here are couple suggestions, but others will have ideas as well. You probably know most/all of this already, but since you asked, and since my kid seemed to enjoy the experience and wants to return again, I will put this out in case any of it is useful.
Take your kid to a trap range several times and get him used to shouldering the gun and shooting. Trap shots are very similar to what you will see on a pheasant hunt. Have him do this with a light jacket and gloves so he can get used to the safety and clothing that he will be wearing. I also taught my son the "swing-through" method of shooting since it seemed to make the most sense and was the easiest for him to learn. The sustained lead approach works as well, but I think even most experts will tell you that the swing through approach is better at the learning stage. You may even have someone that is a good wingshot give him a lesson or pointers. Don't know about you, but in my sons eyes I am not the most intelligent human he has ever met:>) and he often listens better if the same message is delivered by somebody else.
Don't get frustrated if they don't figure it out right away. In my son's first 5-day hunt in SD I think he killed 7-9 birds, not a limit, but he was happy for each bird that dropped. It takes a little while before they learn to become "hunters" and not hikers or followers. There is a fair amount of skill involved in walking along and looking for flushes behind a dog (watching the dog, looking for holes in the ground, placing their feet, getting the gun up, ID'ing the bird, etc.). Pheasants are not very fast flyers, and they seem like big softballs after you have shot a few hundred of them, but good hunters and shooters often underestimate how hard it is when a person, especially a kid, first starts hunting them. Also, kids don't usually understand what a "birdy" dog looks or acts like (unless you have pointers) and they often don't understand what it means to "follow the dog." This leads to my second point.
Use a dog if you can. Everyone on this list has an opinion about the best dog breed for hunting. Personally, I hunt with labs, but the other breeds work just as well for each owner. The important thing is to hunt with a well-trained dog. The kids love following the dog and it makes it much more enjoyable and entertaining. Yes, you can kill a limit of pheasants in SD by just walking along and hunting, but without a dog you never know when the flush will come and it can get boring if you have walked awhile and not seen any birds. It is also not as entertaining. With even a mediocre dog you will at least be covering a lot more ground and know that you didn't walk by as many birds. But this only works if you don't have a dog that flushes wild and is not trained to obedience. A good dog will also help you find more cripples, which is especially important when hunting with a kid since they will not be as good a shot and will not hit many birds as well as a more skilled shooter will.
I used to walk with no gun behind my son when he first started hunting. I could keep an eye on him and watch/work the dog and give him some pointers. However, this made him nervous and didn't work perfectly, but I think it was a good compromise. I also felt safer since a young kid can get awfully excited and swing his gun in the wrong direction when the birds start to flush. Now that my kid is older I trust him to go off on his own a ways with a dog and find his own birds. Last year he did great and he is gaining confidence and skill that will be useful when he is in a bigger group of folks. But I still would not want him hunting in a large group with a lot of confusion. IMO I think their first hunt should not be in a cornfield with 20 other people, dogs running crazy, and pheasants flying all over the place. Keep it a simple walk with just a couple of you to keep it less confusing. Just my humble opinion. A lot of that depends on how much he hunts.
I also found hunting in October and early November was better since he didn't have to fight with big gloves, hats, boots, and jackets. the weather, as a rule, is usually much more enjoyable. The birds also seem to hold a little better. Busting through snow drifts in 15 deg temps, 20mph wind, with full winter gear in December is sometimes a little much for me, let alone a 13-yr old. Remember, you want him to return next year. Yeah, late Dec hunting can be magical, especially if it is calm and you just had some snow, but often it can be brutal. For every magical day there is often 5-10 days of suffering looking for that 3rd bird. This builds character, but you can only build so much character in a 13 year old before they decide playing Playstation is more enjoyable.
My last tip is to try and hunt linear cover for the first few times. Instead of marching out into a field where flushes can come from 360 deg I had my kid walk fencerows, ditches, shelter belts and small, narrow fields. Or I at least put him along the edge of a larger field to reduce the directions a bird could flush from. This helped reduce the amount of time he needed to ID the bird, plant his feet, shoulder the gun, swing through and shoot. It just made it easier since he didn't have to look in all directions for the dog, me, and the bird. Once they figure it all out they can graduate to those big open fields or WPAs that stretch on for miles in all directions.
Just my $0.02 worth. Main thing is to go and make it fun and exciting.