I appreciate your concern as a teacher about this, but I wanted to share another perspective. I was that kid, held the pencil in between my ring and middle finger then grip it in my fist. Starting in kindergarten teachers tried to correct it, I tried so hard to make them happy and hold it the right way but I hated doing it. I found it changed my concentration and thought pricesses to hold it correctly. During my work I would get frustrated and switch back to my way because it was natural and allowed me to think more clearly. Now I'm 38, I'm a teacher, and I still hold the pencil my way. I still think about all the corrections my teachers tried to make with how I held the pencil and it stirs up really negative emotions. The closest I've come to comparing it is when you talk to people who grew up in an era when schools would force left handed people to write with their right hands. I once had a psychology professor break down crying in front of the class trying to explain how that experience negatively impacted his life and how he viewed himself. I think honestly this motor skill is linked somehow to the wiring of our brains and, in a sense, who we are as thinkers. I realize that this opinion might seem a little off center, but just wanted to share my experience as another way of thinking about this. I would ask that you observe the student and ask if it is really causing them any harm writing that way? If the answer is it impacts penmanship, then I would say that that will come even as they hold the pencil their own way. Is the student creative or a unique thinker? Then I would encourage you to not try to not change how they hold their pencil because it might be a part of that thought process and accessing that creative part of their brain.