By youngster, how old are we talking? If he hasn't mastered direct-reining, you shouldn't make the transition to neck-reining just yet! :) Just make sure he's MASTERED left and right without head-tossing before you go confusing him with the different pressures of neck reining.
Remember, when you are neckreining a horse, you are putting pressure on the outside. I've seen people do lots of different things, like crossing the reins on the bit (you hold the rein connected to the left side of the bit in your right hand, and vice versa) and teaching them to recognize the pressure on their neck as turning (make sure you use leg aids as well). I've also seen people use hackamores because they don't put pressure on a specific side of the mouth.
Can you tell us a little more about the way the horse is trained? :)
I'm so busy, I don't know if I've found a rope... or lost my horse...