I am about to take up jumping lessons on another horse. My own horse is recovering from stomach ulcers and can't be ridden, plus he is relatively new to jumping. Therefore, I will take a few lessons on this jumping horse to work on my own jumping position. I think it is a splendid idea to take lessons on another horse, as lesson horses are meant to be teachers. When I ride a lesson horse, I can focus more on myself because the lesson horse is experienced and solid. With my horse, I have to focus more on him because he has a lot to learn. Lesson horses also work wonders for riding confidence. I ride one particular lesson horse every Sunday for free, to get the "kinks" out of him after his week of schooling beginning riders. With my own horse, I ride him with my trainer because that helps my horse and I more than if I were riding a lesson horse. It all depends on what you want to accomplish. If you want to work mainly on yourself, or work on something that is new before you try it on your own horse, then a lesson with a lesson horse is a great idea. If you want to improve your horse and your horse and you as a pair, then riding your own horse in a lesson is a wiser option.