Most horsepeople understand that horses should be started in the snaffle and most even have a basic idea of why this is correct but, I'd like to review it a little anyway to make sure it really makes sense.
A snaffle has direct contact only, not leverage. It works primarily off the corners of the horse's mouth and puts some pressure on the tongue. A snaffle is easy for a horse to learn to accept and learn to pick up and carry in his mouth. It's easy for the rider too because it works well with primary rein cues (i.e. direct rein and opening rein). It also works well with alternating reins. All in all, it's good basic education for the horse.
Now, a horse must learn to "give" to the snaffle too. He must learn to turn and follow the rein around, backing up and having a nice easy stop with no resistance. All of this is very important before he transitions to a curb bit. I want a horse to be able to collect up at all gaits and in all transitions. He should also circle well at all gaits (and I mean circles - not eggs or stop signs!). The horse should show no resistance at all, he should not push on the bridle or root or elevate his neck. All should be soft and pretty.
I like to teach all young snaffle bit horses basic things like side passes, counterbends and flexing to the side. Serpentines and spirals are nice exercises too. This work is all based on that circle work done earlier in the training process. (It really works too, to remember these exercises and make them an ongoing part of your horse's training and warm-up program. They should never go away.)
Only when a horse has accomplished all of the above do I think he's ready for the next step. If the horse is a junior horse, I will move him to a hackamore next. A hackamore gives nice indirect leverage and with two hands. The horse must learn to do all of those basic maneuvers in this new piece of equipment. He starts to understand the "lift" and the feel of leverage and I think it helps a junior horse learn to respond softly and confidently to the curb.
If the horse is six years or older though, I'll put him a very mild, jointed and limber curb bit with short curved shanks. And......the process starts all over again! I think its so important that the horse learns and gains confidence as he progresses through each layer of training so I think of the transition from snaffle to bridle as a series of building blocks, one on top of another. Hope this helps! Talk to you next week, JD.