It does raise eye brows because he is a big kid anyway. But, I have simply told him that in school he would be in 4th grade, and in some subjects at home he is working at that level or higher. In others, not so much so we call him a third grader. He isn't in anything this year that requires a grade, but if he was I would list the grade of his age. He is the youngest and because his siblings are all a lot older he has been told how each of them had challenges when they were younger. He can see that they are all fine now so its a non issue for him. I've seen kids make huge strides in one school year so I wouldn't worry too much now. By high school you may be ready to put him back up to his "real" grade. If not so what? When he is 30 no one will know or care that he graduated high school at 19.