How do I train a horse that breaks gait during a western pleasure class?

A horse that breaks gait — dropping from a jog to a walk, or from a lope to a jog, during the class — is committing one of the most obvious and most penalized errors in western pleasure, and the cause of the break determines the correct training response. Breaks that happen because the horse was never confirmed at the required pace are training gaps. Breaks that happen because the pace has been trained so slowly that the horse cannot maintain the gait without falling out of it are a consequence of over-training the slow pace before the horse had the physical strength to sustain it. And breaks that happen because the horse is distracted or anxious are environmental and behavioral rather than purely technical. For a horse that breaks gait due to an undertrained slow pace, the correction is to work slightly above the pace that produces breaks until the horse can sustain that pace confidently, then gradually approach the competition pace from the correct foundation. A horse that breaks every time it reaches the competition pace needs more time at a slightly faster pace rather than drilling at the pace that produces failure. Success builds the physical strength and rhythm that allows the slower pace to eventually be sustainable. For a horse that has been trained so slowly that the gait loses its mechanical correctness and eventually collapses into a break, rebuilding with more forward energy is the correction. Going back to a working jog or working lope and confirming the horse's ability to maintain those paces with energy and correct footfall before attempting to slow them down produces a more sustainable foundation than attempting to slow a pace that was never truly confirmed. Preventing breaks in competition requires a rider who monitors the horse's energy level throughout the class and makes subtle adjustments before the break happens rather than correcting it after. A horse that is beginning to trail off in energy will break gait within a few strides if not addressed; a quiet leg aid that refreshes the horse's forward energy before that happens prevents the break entirely.