Are you from the school or are you this child's parent? Either way, I think the school and the parent need to have a conversation. Ultimately, the parent needs to decide what is required and help the school develop a plan to guarantee that the parents' wishes are followed.
If the parent insists on wearing the orthotics as prescribed, the school needs to find a way to do that. Maybe the parents need to develop consequences for the child if he refuses to wear them (take away TV, favorite toys, dessert, etc - something that will upset the kid enough so that he will wear them in order to avoid the penalty).
I also think that there are times that adults need to truly act like adults and insist that rules be followed. Don't put up with the child refusing to wear them, just as you wouldn't put up with a child at school who refused to sit quietly at their desk when it was time to work. The teacher/therapist needs to force the child to wear them, even if it means putting them back on every 10 seconds. Eventually, the child will learn that fighting is futile and the orthotics will stay on.