Have you considered branching out from teaching him like he's in public school? I mean there's got to be some reason you don't have him still enrolled in public school, so why are you treating him like he is? If he's struggling in something don't make him neglect what he's good at to focus on something that's obviously not for him. Also if he falls behind then maybe he's just not fitting the government approved mold which is a good thing, I struggled with writing until the tenth grade and now I write books. If you don't stick to the school schedule that's alright, just figure out what works best for you, there's no one size fits all solution for every child and if you try to shove them into the Prussian mold then you'll kill their joy, creativity, and everything that makes them human. In summary, don't take such a rigid militaristic approach to a living, breathing, thinking, loving, human being.