How do I develop correct large fast and small slow circles in a reining pattern?

The reining circles are judged on the horse's ability to demonstrate a clear and obvious distinction between the large fast circle and the small slow circle — not just a slight variation in pace, but a genuinely dramatic difference in speed and size that shows the horse is responsive to the rider's aids across a wide range. A horse that lopes the large circle only slightly faster than the small one, or that runs the large circle without true forward drive, is leaving significant points on the table regardless of how correct its other maneuvers may be. The large fast circle is built on impulsion, straightness, and the horse's willingness to open its stride when asked. Training it requires that the horse understand a forward-driving leg aid that means increase pace — not a leg that means hold pace, not a leg that means move over, but specifically one that means go forward with energy. Many horses that are schooled heavily on collection and responsiveness become reluctant to open up in the large circle because forward pressure has always meant something else. Teaching a clear, consistent cue for increased pace — and rewarding the horse when it responds by truly driving forward — resolves this over time. The small slow circle develops from the horse's ability to collect, carry weight on its hindquarters, and maintain a controlled pace without resistance or tension. It should feel like the horse is on a loose, easy collection rather than being held back. A horse that is pulled into the small circle will show tension in its neck and tail, while a horse that truly understands collection will organize itself without significant rein pressure. The transition between the two circles is where the horse demonstrates its training most clearly. A smooth, immediate change from slow to fast — or fast to slow — that happens in one or two strides is the mark of a horse that is genuinely responsive to its rider.