Jeremy,
I am humbled and proud that you took time with your son. My son is now 23 and never took up a serious interest in foosball. It is too bad because he has some real nice natural skills including playing smart. I spent time with both my kids when they were little (my second is a girl who will be 25 on Christmas eve).
It is difficult for me to recommend to starting players to shoot a backpin even though I love it and think it is the best shot on the table. I am up front, probalby to a fault, to tell people it is not only the best shot but it is the hardest shot to learn. It takes a big commitment to get the shot tournament ready. This is not true with a rollover. The overall learning curve is shorter (much shorter) and you get almost instant gratification. It goes booom and looks cool. Any time you have spectators and they see a just a decent rollover they oooh and ahhh.
The the basics of a rollover are simple, long both ways and a straight. Now there is much more that can be done but even in its most complex mature form it is only a fraction of what a mature backpin has to deal with.
The natural release of a rollover is far superior to any other shot and this release alone makes it dangerous even in the hands of a novice.
Still, maybe someday, a young creative phenom will see all the benefits and make the commitment to develop a backpin. When I was young, motivated, and had the time (now I am old, motivated, and don't have time) I wanted to develop a game that was unique and I wanted to find new boundries and take the game to places it had never been. That was my dream for foosball.
This is what I would try and tell your son if I could. To let him know that he could leave his mark on the history of foosball. Foosball is still a young "sport" (or game) and we have not seen how far it can go. Fred C. has taken the game to a new place but there is another like Fred out there right now. Someone who will (and can) dedicate their life to the advancement of foosball. It has to be a person with a pure desire and drive because they will need to do for the love of the game and not for money. Like an artist or like early golfers, basketball players, baseball, football, etc.
As totally outstanding as Fred has been and all that he has accomplished (far far far beyond anyone else in the sports short history) I think it can go further. I understand that FC doesn't practice any more except leading up to big tournaments. I want to see someone like FC push and push well into his thirties practicing like they did when they were developing. My gosh, who knows what FC would discover in the game. FC is the closest but there is another out there now, maybe your son, who can rewrite foosball history and do it shooting a backpin.
ahhhh, we will see...maybe in my lifetime, just maybe
Charles