This is Charm, my 31" tall mini boy. He turned 4 this year and met the harness. He has been doing amazingly well!! We've been playing with lots of prep work, standing still, zone 5 driving, voice cues, friendly game with the cart, and pushin into the traces.
Today he pulled it around the outside of the round pen, around the barn, and to the front pasture. At first he was confused that he could push into the shafts to move it, but before I hitched him, I connected him to a drag I made of 2 carrot sticks and some small wood pieces, he got the concept much quicker.
Tomorrow our next step is to start adding weight to the cart, and then me getting in!!