I'll chime in here. I'm left handed, but I learned on a right handed bass. I suppose I'm sort of ambidextrous, but I think it's only out of necessity. I can only write with my left handed, though. I am actually glad I learned on a right handed bass because I'm able to pick up any bass and play it. I also use a three and four finger plucking technique pretty successfully, I'm able to tap, finger pick (the guitar type finger picking) chord with my fretting hand, and all this without too much mud. he just needs to practice. when I first got my bass, I was pretty much inseparable with it. I played something like 6 hours a day, at least. I just started hanging out with that chunk of wood, and I never really put it down. I can never be sure if I was ever "stunted" by learning right handed, but it doesn't seem that way. I've been able to pick out some Frank Zappa melodies, Dream Theater, Billy Sheehan, and St. Vincent stuff and play it without problems. also, a little bit of Bach, but it's more tapping stuff. but yea, I suppose unless he is just overly dominant with his left hand (which I assumed he would be when he's young), it may be better to teach him right handed just due to the fact that there's so many more choices available to him.