How long should early training sessions be for young horses and how do you know when to quit?

Session length for young horses is one of the most consistently misjudged variables in colt starting, and the error is almost always in making sessions too long rather than too short. Clinton Anderson, Pat Parelli, and Warwick Schiller all advocate shorter, more frequent sessions over longer, less frequent ones — though for different reasons. Anderson's practical standard for young horse sessions is based on achieving a specific training goal and ending there rather than filling a predetermined time block. A session that accomplishes its goal in fifteen minutes should end at fifteen minutes. A session where the horse has softened, improved, and shown genuine try should end on that positive note regardless of how much time has elapsed. Continuing a session past the point of genuine progress typically produces a tired, frustrated horse that ends on a worse note than it could have ended on twenty minutes earlier. He identifies ending on a good note as one of the most important skills in training young horses — not ending when the horse demands to stop, not ending when the trainer is satisfied the horse has worked enough, but ending when the horse has made a genuine positive try on whatever was being worked on. This requires the trainer to recognize tries rather than only performances. Warwick Schiller's reasoning for shorter sessions draws on nervous system science: a young horse's capacity to process new information and make new associations is limited, and sessions that continue past the horse's processing capacity produce habituation to pressure rather than learning. Short sessions with adequate rest between them allow the brain to consolidate what was experienced, which is when genuine learning occurs. Parelli's guideline for session length is horse-specific — he watches for the horse's processing signals as the indicator of when genuine learning is happening and when it has stopped. Licking and chewing, yawning, and blinking indicate processing. A horse that stops showing these signals and begins to look dull or mechanical has moved from learning to enduring.