Teaching a horse to pick up the right lead can be accomplished several different ways. Often, what works to teach one horse to pick up the correct lead won't help the other pick up leads right, but by trying several different methods you will learn what works best to make sure your horse gets the right lead every time- whether in the arena, on the trail, or at a horse show. Below are described several methods which may work to teach your horse to pick up the correct lead.
1. Make your cues clear and consistent, and your corrections as immediate as possible. To cue for the canter on the average horse, sit deep in the saddle (do not lean forward), and slide your outside leg back several inches. For direct reined horses, it is also important to maintain contact on the outside rein. Advanced riders also thrust their pelvis to the inside when cuing the horse to canter on the inside lead, and time the cue of their outer leg to just before the horse's outside hind hits the ground. These more specific cues help clarify the request to the horse.
2. Natural Bend - When a horse is moving around a corner or on a circle, the natural bend of the body will usually make the horse pick up the correct lead automatically. Many trainers only ask young horses for a canter transition when in a corner, to help the young horse understand. After becoming accustomed to picking up the correct lead on a corner, begin asking as you approach a corner, and gradually begin asking on straightaways.
3. Stop and Praise - The clearest way to communicate to a horse they've done the correct behavior is to immediately let them quit work. With particularly confused horses this is an effective way to tell them they're right when they do pick up the correct lead, and motivate them to pick it up correctly in the future.
To do this method: Cue for canter, if lead is wrong immediately correct strongly and transition down. If the horse picks up the correct lead, praise loudly, allow horse to canter a short distance on correct lead, then transition down and immediately dismount and loosen girth. Several sessions of correct lead = end of work quickly reinforces picking up the correct lead.
4. Jump into Canter - Intermediate or Advanced riders can use a small jump to help teach a stubborn or particularly one-sided horse to pick up the correct lead. Set the jump at a height that will motivate the horse to take a small jump instead of trot over (usually about 2ft) place the jump several strides from the corner of a fenced arena, trot towards the jump, and the horse will naturally land in a canter. The rider should praise the horse if they land and canter the corner on the correct lead, and not break gait for as long as the horse is able to hold it. (cantering on the correct lead for a one-sided horse is demanding, and muscle should be built through increasing durations of cantering on that lead) over a course of weeks and months, the jump can be removed, replaced with a single groundpole, and eventually the horse can be taught to pick up the canter at that point with no aid, and later, once the cues are taught, asked to pick up the right lead anywhere.