The rein back is first introduced at Second Level. The time to teach the rein back is when your horse is accepting the contact and stays on the aids through all three gaits as well as the transitions. The horse is also starting to understand the concept of yielding to the rein when pushed forward into the contact. This could be when you are in Training or First level.
First, introduce the rein back from the halt. In the beginning it is not as important that the rein back is perfectly straight but that the horse figures out the aids and responds in the correct way of stepping in reverse. Once the horse understands and accepts the aids for rein back then we can look after the details of straightness, even diagonal steps, length of strides and number of steps.
Aids for the rein back:
1. Starting from an immobile halt the rider lightens their seat by tipping forward slightly and letting both legs come back behind the girth.
2. In this position the rider will push the horse forward into the contact.
3. When the horse pushes into the contact he should yield to the pressure and step backwards.
In the beginning, it’s ok to allow the horse to halt so you can reward the horse for their effort. As a finished product you would like to go from the rein back directly into the walk without the halt. You can work on this later once they get the idea and become proficient at the rein back from a halt. To go forward again the rider will sit back in the normal position, and both legs will return back to the girth pushing the horse forward into a soft contact allowing the horse to step ahead.
Watch Sidney, a 6 yr old OTTB, who is learning rein back for the first time.
Another common way of teaching the rein back with with someone on the ground. Either with their hand or whip, apply some pressure on the horses chest. This can help the horse understand the rein back aids at the same time the rider is asking for the rein back. I will do this if the horse does not understand the aids the first time we ask. It is not always necessary to have a ground person assist you as you can see in this video of Sidney learning the rein back for the first time.
Lots of praise for a good effort and they will try harder next time. In a blink they will have learned the aids!