You're correct to use placing rails, which offer an excellent schooling tool for training jumpers. Using them will certainly teach your horse to wait for his fences and find comfortable distances. However, prior to using placing rails before a jump, your horse should already have been schooled over simple ground poles. Your youngster seems to lack this education so take the time to fill in this gap in his training. Start by introducing a single pole on the ground. Go back and forth over this several times, first at a walk, then at a trot. Always approach the pole off a square turn and ride a straight line to the center of the pole. Then add a second pole, five to six feet away from the first. (adjust the distance depending on the horse's stride.) Repeat adding poles, three, and four. Never allow your horse to hurry over the poles; he must maintain an even walk, then trot rhythm, when approaching, going over and moving away from the poles. Only when your horse calmly and quietly trots all three/four poles, dead center, and straight-a process that may require several training sessions-should you reintroduce a jump to the scenario. Add a cross-rail, eight to nine feet after the last trotting pole. Then trot the exercise, again focusing on riding straight and maintaining an even rhythm throughout. When your horse completely understands the concept of dealing with poles before a fence, you can remove the first, then the second ground pole, so eventually you'll trot just one placing pole before the fence. When your horse stays completely relaxed through this simple placing-pole-to-to-cross rail exercise you can consider increasing the difficulty of the jump.
This article written here with permission from trainer Annie Eldridge, Horse Illustrated July 2003 issue.