Have him do them from the ground first one pole, and at walk, then trot, then two at walk then trot etc.
The horse is lacking in confidence.
If she wants to stop and sniff always let her and don't push her in the poles, if she doesn't want to do them maybe at trot, try again at walk.
I used to ride an off track mare who though every pole was a 4 foot jump that had to be taken at a gallop. What worked best for her was having random poles laid out at all angles in the ring. I would be completely relaxed and ride her as if nothing was there at all. After about the fifth or sixth one, she started to realize there was no reason to fuss over them. She was happily working over the poles with no issue. Throughout the ride, I had some friends start to line them up one at a time and work her over and around them. I found that it helped calm her down because they weren't immediately in a line and she wasn't pointed directly at them as if a "here they are, go do this" kind of thing. We kept doing that same routine for about 3 weeks until she could completely relax going into a line of them in the middle of the ring. I also tried to change direction as often as possible as well as doing tons of circles, serpentines, random shapes etc.