Maybe try Lounging over jumps and tell him or her easy. You want them to know that you are in control. I have a horse that started out the some way and it took me 2 months to get him to understand that he needs to slow down. Or maybe you can try halk halting over the jumps. I would not stop him after a jump becaus ethat is only teaching him that it is ok to stop after a jump and it is not teaching him to slow down. Trust me I have gone throughit all!!