It is necessary that both hind legs move simultaneously and identically in both carrying and pushing manner while doing School jumps. Only few horses have two symmetrical hind legs. Most horses tend to put less weight on one hind leg and move the stronger hind leg further forward.
It is important for the rider to recognize this asymmetry from the beginning of the training. By training the horse straight, the weak hind leg can be made stronger so that the horse is later capable of using both hind legs equally.
The High School exercises were already used in ancient Greece to show the skills of horse and rider and in times of war, the exercises were used as defense.
In the 17th and 18th century, the exercises were further developed as an art form.
At the end of the 18th century, the armies of Napoleon made the baroque glory come to an end.