In horse racing, how do they determine which horse goes into the various positions of the starting gate?

In most races, they draw a horse's name and then draw a post position. In the Derby, they draw a horse's name, and the horse's connections get to choose their post from the posts not taken. This brings a little more drama to the draw for post position and gets the trainer strategizing.

Connections for horses are brought together for a meeting of sorts. The horses names are called and the connection for that horse chooses what post position he chooses. Some post positions are better for some horses than others. It depends on the horses style of running, training, etc. Usually the best post positions are between four and eight. But some horses can benefit from other post positions as well. For instance, last year Bib Brown drew the 20th position for the Derby. He is the first horse to win the Derby since Clyde Van Dusen in 1929

I had this problem with one of my horses. So I started on the ground by leading my horse in a large circle in which we had to pass a partially opened gate. We made him pass so that we would be walking into the opening if the gate were swung all the way open. My husband would stand by the gate and open and close it in small increments as we were walking our circle. The key is to keep the horse moving so that the majority of his attention is on you and walking. He will notice the gate and may even shy away from it but as you ignore it and keep him moving he will relax more and more as he goes by it. As he relaxes move him in tighter to the gate (closer) and every other turn or so try to walk him thru the gate. Now here is where you have to time it right. If you pause and don't keep him moving it will be easier for him to balk on you and stop or back away. If he only goes a little bit thru and then stops move him out quickly and start again. It needs to be "easier" for him to go thru the gate then to stop and back away. He will eventually realize that it is more work to keep walking then it is to go thru the gate and get a reward. Reward him by letting him rest and a few rubs. Never reward with treats because that will create a bigger problem in the end. Once you master it on the ground then do it while riding him. Always remember that when a horse misbehaves and you don't correct it it will only get worse. Horses are like kids and will try to get away with as much as we allow them. Your horse realized being in the arena was work and he is trying to find a way out of that. Good luck!